diff --git a/devtools/client/debugger/images/moz.build b/devtools/client/debugger/images/moz.build
index d362551ff07a..bc6f2d406dd5 100644
--- a/devtools/client/debugger/images/moz.build
+++ b/devtools/client/debugger/images/moz.build
@@ -46,5 +46,6 @@ DevToolsModules(
     'stepOver.svg',
     'tab.svg',
     'whole-word-match.svg',
+    'window.svg',
     'worker.svg',
 )
diff --git a/devtools/client/debugger/images/window.svg b/devtools/client/debugger/images/window.svg
new file mode 100644
index 000000000000..3dc00bddd14a
--- /dev/null
+++ b/devtools/client/debugger/images/window.svg
@@ -0,0 +1,4 @@
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+   - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16"><path fill="context-fill" d="M13 1H3a3 3 0 0 0-3 3v8a3 3 0 0 0 3 3h11a2 2 0 0 0 2-2V4a3 3 0 0 0-3-3zm1 11a1 1 0 0 1-1 1H3a1 1 0 0 1-1-1V6h12zm0-7H2V4a1 1 0 0 1 1-1h10a1 1 0 0 1 1 1z"></path></svg>
\ No newline at end of file
diff --git a/devtools/client/debugger/src/actions/navigation.js b/devtools/client/debugger/src/actions/navigation.js
index cfc0559e7577..1a066e727074 100644
--- a/devtools/client/debugger/src/actions/navigation.js
+++ b/devtools/client/debugger/src/actions/navigation.js
@@ -58,7 +58,7 @@ export function connect(url: string, actor: string, canRewind: boolean) {
     dispatch(
       ({
         type: "CONNECT",
-        mainThread: { url, actor, type: -1 },
+        mainThread: { url, actor, type: -1, name: "" },
         canRewind
       }: Action)
     );
diff --git a/devtools/client/debugger/src/actions/source-tree.js b/devtools/client/debugger/src/actions/source-tree.js
index 410acbc91a35..b2cfa0c44b2c 100644
--- a/devtools/client/debugger/src/actions/source-tree.js
+++ b/devtools/client/debugger/src/actions/source-tree.js
@@ -3,27 +3,12 @@
  * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
 // @flow
 
-import type { Action, FocusItem, ThunkArgs } from "./types";
-import type { Context } from "../types";
+import type { TreeNode } from "../utils/sources-tree/types";
 
-export function setExpandedState(thread: string, expanded: Set<string>) {
-  return ({ dispatch, getState }: ThunkArgs) => {
-    dispatch(
-      ({
-        type: "SET_EXPANDED_STATE",
-        thread,
-        expanded
-      }: Action)
-    );
-  };
+export function setExpandedState(expanded: Set<string>) {
+  return { type: "SET_EXPANDED_STATE", expanded };
 }
 
-export function focusItem(cx: Context, item: FocusItem) {
-  return ({ dispatch, getState }: ThunkArgs) => {
-    dispatch({
-      type: "SET_FOCUSED_SOURCE_ITEM",
-      cx,
-      item
-    });
-  };
+export function focusItem(item: TreeNode) {
+  return { type: "SET_FOCUSED_SOURCE_ITEM", item };
 }
diff --git a/devtools/client/debugger/src/actions/sources/tests/blackbox.spec.js b/devtools/client/debugger/src/actions/sources/tests/blackbox.spec.js
index 0cdb62a9fb1b..d722711a87d6 100644
--- a/devtools/client/debugger/src/actions/sources/tests/blackbox.spec.js
+++ b/devtools/client/debugger/src/actions/sources/tests/blackbox.spec.js
@@ -30,16 +30,10 @@ describe("blackbox", () => {
       throw new Error("foo should exist");
     }
 
-    const { thread } = selectors.getSourceActorsForSource(
-      getState(),
-      foo1Source.id
-    )[0];
-    const displayedSources = selectors.getDisplayedSourcesForThread(
-      getState(),
-      thread
+    const displayedSources = selectors.getDisplayedSources(getState());
+    expect(displayedSources.FakeThread[fooSource.id].isBlackBoxed).toEqual(
+      true
     );
-
-    expect(displayedSources[fooSource.id].isBlackBoxed).toEqual(true);
     expect(fooSource.isBlackBoxed).toEqual(true);
   });
 });
diff --git a/devtools/client/debugger/src/actions/tests/setProjectDirectoryRoot.spec.js b/devtools/client/debugger/src/actions/tests/setProjectDirectoryRoot.spec.js
index ac32677dea95..2801432b7e25 100644
--- a/devtools/client/debugger/src/actions/tests/setProjectDirectoryRoot.spec.js
+++ b/devtools/client/debugger/src/actions/tests/setProjectDirectoryRoot.spec.js
@@ -11,8 +11,6 @@ import {
   makeSource
 } from "../../utils/test-head";
 
-import type { Source } from "../../types";
-
 const { getProjectDirectoryRoot, getDisplayedSources } = selectors;
 
 describe("setProjectDirectoryRoot", () => {
@@ -54,14 +52,15 @@ describe("setProjectDirectoryRoot", () => {
     dispatch(actions.setProjectDirectoryRoot(cx, "localhost:8000/examples/js"));
 
     const filteredSourcesByThread = getDisplayedSources(getState());
-    const filteredSources = Object.values(filteredSourcesByThread)[0];
-    const firstSource: Source = (Object.values(filteredSources)[0]: any);
+    const filteredSources = (Object.values(
+      filteredSourcesByThread.FakeThread
+    ): any)[0];
 
-    expect(firstSource.url).toEqual(
+    expect(filteredSources.url).toEqual(
       "http://localhost:8000/examples/js/scopes.js"
     );
 
-    expect(firstSource.relativeUrl).toEqual("scopes.js");
+    expect(filteredSources.relativeUrl).toEqual("scopes.js");
   });
 
   it("should update the child directory ", () => {
diff --git a/devtools/client/debugger/src/actions/tests/source-tree.spec.js b/devtools/client/debugger/src/actions/tests/source-tree.spec.js
index a52f5cb40cc3..fcbd56da33f5 100644
--- a/devtools/client/debugger/src/actions/tests/source-tree.spec.js
+++ b/devtools/client/debugger/src/actions/tests/source-tree.spec.js
@@ -12,8 +12,8 @@ describe("source tree", () => {
     const { dispatch, getState } = createStore();
     const expandedState = new Set(["foo", "bar"]);
 
-    expect(getExpandedState(getState(), "FakeThread")).toEqual(undefined);
-    dispatch(actions.setExpandedState("FakeThread", expandedState));
-    expect(getExpandedState(getState(), "FakeThread")).toEqual(expandedState);
+    expect(getExpandedState(getState())).toEqual(new Set([]));
+    dispatch(actions.setExpandedState(expandedState));
+    expect(getExpandedState(getState())).toEqual(expandedState);
   });
 });
diff --git a/devtools/client/debugger/src/actions/types/index.js b/devtools/client/debugger/src/actions/types/index.js
index a778c8bbc6ce..6d6f13c6ffcc 100644
--- a/devtools/client/debugger/src/actions/types/index.js
+++ b/devtools/client/debugger/src/actions/types/index.js
@@ -71,10 +71,7 @@ type NavigateAction =
   | {| +type: "CONNECT", +mainThread: MainThread, +canRewind: boolean |}
   | {| +type: "NAVIGATE", +mainThread: MainThread |};
 
-export type FocusItem = {
-  thread: string,
-  item: TreeNode
-};
+export type FocusItem = TreeNode;
 
 export type SourceTreeAction =
   | {| +type: "SET_EXPANDED_STATE", +thread: string, +expanded: any |}
diff --git a/devtools/client/debugger/src/client/firefox/create.js b/devtools/client/debugger/src/client/firefox/create.js
index 19df8ec6d57d..693d56027fce 100644
--- a/devtools/client/debugger/src/client/firefox/create.js
+++ b/devtools/client/debugger/src/client/firefox/create.js
@@ -77,6 +77,7 @@ export function createWorker(actor: string, url: string) {
     actor,
     url,
     // Ci.nsIWorkerDebugger.TYPE_DEDICATED
-    type: 0
+    type: 0,
+    name: ""
   };
 }
diff --git a/devtools/client/debugger/src/components/PrimaryPanes/SourcesTree.js b/devtools/client/debugger/src/components/PrimaryPanes/SourcesTree.js
index b2bb5533e317..34409f3e0e9e 100644
--- a/devtools/client/debugger/src/components/PrimaryPanes/SourcesTree.js
+++ b/devtools/client/debugger/src/components/PrimaryPanes/SourcesTree.js
@@ -16,10 +16,8 @@ import {
   getDebuggeeUrl,
   getExpandedState,
   getProjectDirectoryRoot,
-  getDisplayedSourcesForThread,
+  getDisplayedSources,
   getFocusedSourceItem,
-  getWorkerByThread,
-  getWorkerCount,
   getContext
 } from "../../selectors";
 
@@ -29,7 +27,6 @@ import { getGeneratedSourceByURL } from "../../reducers/sources";
 import actions from "../../actions";
 
 // Components
-import AccessibleImage from "../shared/AccessibleImage";
 import SourcesTreeItem from "./SourcesTreeItem";
 import ManagedTree from "../shared/ManagedTree";
 
@@ -42,25 +39,25 @@ import {
   nodeHasChildren,
   updateTree
 } from "../../utils/sources-tree";
+import { parse } from "../../utils/url";
 import { getRawSourceURL } from "../../utils/source";
 
-import { getDisplayName } from "../../utils/workers";
-import { features } from "../../utils/prefs";
-
 import type {
   TreeNode,
   TreeDirectory,
   ParentMap
 } from "../../utils/sources-tree/types";
-import type { Worker, Source, Context } from "../../types";
-import type { SourcesMap, State as AppState } from "../../reducers/types";
+import type { Source, Context, Thread } from "../../types";
+import type {
+  SourcesMapByThread,
+  State as AppState
+} from "../../reducers/types";
 import type { Item } from "../shared/ManagedTree";
 
 type Props = {
   cx: Context,
-  thread: string,
-  worker: Worker,
-  sources: SourcesMap,
+  threads: Thread[],
+  sources: SourcesMapByThread,
   sourceCount: number,
   shownSource?: Source,
   selectedSource?: Source,
@@ -70,8 +67,7 @@ type Props = {
   selectSource: typeof actions.selectSource,
   setExpandedState: typeof actions.setExpandedState,
   focusItem: typeof actions.focusItem,
-  focused: TreeNode,
-  workerCount: number
+  focused: TreeNode
 };
 
 type State = {
@@ -84,17 +80,24 @@ type State = {
 
 type SetExpanded = (item: TreeNode, expanded: boolean, altKey: boolean) => void;
 
-class SourcesTree extends Component<Props, State> {
-  mounted: boolean;
+function shouldAutoExpand(depth, item, debuggeeUrl) {
+  if (depth !== 1) {
+    return false;
+  }
 
+  const { host } = parse(debuggeeUrl);
+  return item.name === host;
+}
+
+class SourcesTree extends Component<Props, State> {
   constructor(props: Props) {
     super(props);
-    const { debuggeeUrl, sources, projectRoot } = this.props;
+    const { debuggeeUrl, sources, threads } = this.props;
 
     this.state = createTree({
-      projectRoot,
       debuggeeUrl,
-      sources
+      sources,
+      threads
     });
   }
 
@@ -104,21 +107,24 @@ class SourcesTree extends Component<Props, State> {
       debuggeeUrl,
       sources,
       shownSource,
-      selectedSource
+      selectedSource,
+      threads
     } = this.props;
     const { uncollapsedTree, sourceTree } = this.state;
 
     if (
       projectRoot != nextProps.projectRoot ||
       debuggeeUrl != nextProps.debuggeeUrl ||
+      threads != nextProps.threads ||
       nextProps.sourceCount === 0
     ) {
       // early recreate tree because of changes
-      // to project root, debugee url or lack of sources
+      // to project root, debuggee url or lack of sources
       return this.setState(
         createTree({
           sources: nextProps.sources,
-          debuggeeUrl: nextProps.debuggeeUrl
+          debuggeeUrl: nextProps.debuggeeUrl,
+          threads: nextProps.threads
         })
       );
     }
@@ -145,6 +151,7 @@ class SourcesTree extends Component<Props, State> {
       this.setState(
         updateTree({
           newSources: nextProps.sources,
+          threads: nextProps.threads,
           prevSources: sources,
           debuggeeUrl,
           uncollapsedTree,
@@ -161,7 +168,7 @@ class SourcesTree extends Component<Props, State> {
   };
 
   onFocus = (item: TreeNode) => {
-    this.props.focusItem(this.props.cx, { thread: this.props.thread, item });
+    this.props.focusItem(item);
   };
 
   onActivate = (item: TreeNode) => {
@@ -170,16 +177,11 @@ class SourcesTree extends Component<Props, State> {
 
   // NOTE: we get the source from sources because item.contents is cached
   getSource(item: TreeNode): ?Source {
-    const source = getSourceFromNode(item);
-    if (source) {
-      return this.props.sources[source.id];
-    }
-
-    return null;
+    return getSourceFromNode(item);
   }
 
   getPath = (item: TreeNode): string => {
-    const path = `${item.path}/${item.name}`;
+    const { path } = item;
     const source = this.getSource(item);
 
     if (!source || isDirectory(item)) {
@@ -187,15 +189,16 @@ class SourcesTree extends Component<Props, State> {
     }
 
     const blackBoxedPart = source.isBlackBoxed ? ":blackboxed" : "";
+
     return `${path}/${source.id}/${blackBoxedPart}`;
   };
 
   onExpand = (item: Item, expandedState: Set<string>) => {
-    this.props.setExpandedState(this.props.thread, expandedState);
+    this.props.setExpandedState(expandedState);
   };
 
   onCollapse = (item: Item, expandedState: Set<string>) => {
-    this.props.setExpandedState(this.props.thread, expandedState);
+    this.props.setExpandedState(expandedState);
   };
 
   isEmpty() {
@@ -230,6 +233,10 @@ class SourcesTree extends Component<Props, State> {
     return sourceTree.contents;
   };
 
+  getChildren = (item: $Shape<TreeDirectory>) => {
+    return nodeHasChildren(item) ? item.contents : [];
+  };
+
   renderItem = (
     item: TreeNode,
     depth: number,
@@ -238,13 +245,15 @@ class SourcesTree extends Component<Props, State> {
     expanded: boolean,
     { setExpanded }: { setExpanded: SetExpanded }
   ) => {
-    const { debuggeeUrl, projectRoot } = this.props;
+    const { debuggeeUrl, projectRoot, threads } = this.props;
 
     return (
       <SourcesTreeItem
         item={item}
+        threads={threads}
         depth={depth}
         focused={focused}
+        autoExpand={shouldAutoExpand(depth, item, debuggeeUrl)}
         expanded={expanded}
         focusItem={this.onFocus}
         selectItem={this.selectItem}
@@ -258,15 +267,15 @@ class SourcesTree extends Component<Props, State> {
 
   renderTree() {
     const { expanded, focused } = this.props;
+
     const { highlightItems, listItems, parentMap } = this.state;
 
     const treeProps = {
       autoExpandAll: false,
-      autoExpandDepth: expanded ? 0 : 1,
+      autoExpandDepth: 1,
       expanded,
       focused,
-      getChildren: (item: $Shape<TreeDirectory>) =>
-        nodeHasChildren(item) ? item.contents : [],
+      getChildren: this.getChildren,
       getParent: (item: $Shape<TreeNode>) => parentMap.get(item),
       getPath: this.getPath,
       getRoots: this.getRoots,
@@ -286,14 +295,13 @@ class SourcesTree extends Component<Props, State> {
   }
 
   renderPane(...children) {
-    const { projectRoot, thread } = this.props;
+    const { projectRoot } = this.props;
 
     return (
       <div
         key="pane"
         className={classnames("sources-pane", {
-          "sources-list-custom-root": projectRoot,
-          thread
+          "sources-list-custom-root": projectRoot
         })}
       >
         {children}
@@ -301,39 +309,8 @@ class SourcesTree extends Component<Props, State> {
     );
   }
 
-  renderThreadHeader() {
-    const { worker, workerCount } = this.props;
-
-    if (!features.windowlessWorkers || workerCount == 0) {
-      return null;
-    }
-
-    if (worker) {
-      return (
-        <div className="node thread-header" key="thread-header">
-          <AccessibleImage className="worker" />
-          <span className="label">{getDisplayName(worker)}</span>
-        </div>
-      );
-    }
-
-    return (
-      <div className="node thread-header" key="thread-header">
-        <AccessibleImage className={"file"} />
-        <span className="label">{L10N.getStr("mainThread")}</span>
-      </div>
-    );
-  }
-
   render() {
-    const { worker } = this.props;
-
-    if (!features.windowlessWorkers && worker) {
-      return null;
-    }
-
     return this.renderPane(
-      this.renderThreadHeader(),
       this.isEmpty() ? (
         this.renderEmptyElement(L10N.getStr("noSourcesText"))
       ) : (
@@ -347,15 +324,13 @@ class SourcesTree extends Component<Props, State> {
 
 function getSourceForTree(
   state: AppState,
-  displayedSources: SourcesMap,
-  source: ?Source,
-  thread
+  displayedSources: SourcesMapByThread,
+  source: ?Source
 ): ?Source {
   if (!source) {
     return null;
   }
 
-  source = displayedSources[source.id];
   if (!source || !source.isPrettyPrinted) {
     return source;
   }
@@ -366,27 +341,19 @@ function getSourceForTree(
 const mapStateToProps = (state, props) => {
   const selectedSource = getSelectedSource(state);
   const shownSource = getShownSource(state);
-  const focused = getFocusedSourceItem(state);
-  const thread = props.thread;
-  const displayedSources = getDisplayedSourcesForThread(state, thread);
+  const displayedSources = getDisplayedSources(state);
 
   return {
+    threads: props.threads,
     cx: getContext(state),
-    shownSource: getSourceForTree(state, displayedSources, shownSource, thread),
-    selectedSource: getSourceForTree(
-      state,
-      displayedSources,
-      selectedSource,
-      thread
-    ),
+    shownSource: getSourceForTree(state, displayedSources, shownSource),
+    selectedSource: getSourceForTree(state, displayedSources, selectedSource),
     debuggeeUrl: getDebuggeeUrl(state),
-    expanded: getExpandedState(state, props.thread),
-    focused: focused && focused.thread == props.thread ? focused.item : null,
+    expanded: getExpandedState(state),
+    focused: getFocusedSourceItem(state),
     projectRoot: getProjectDirectoryRoot(state),
     sources: displayedSources,
-    sourceCount: Object.values(displayedSources).length,
-    worker: getWorkerByThread(state, thread),
-    workerCount: getWorkerCount(state)
+    sourceCount: Object.values(displayedSources).length
   };
 };
 
diff --git a/devtools/client/debugger/src/components/PrimaryPanes/SourcesTreeItem.js b/devtools/client/debugger/src/components/PrimaryPanes/SourcesTreeItem.js
index 4f9719f07e0c..68a5b2dc2e01 100644
--- a/devtools/client/debugger/src/components/PrimaryPanes/SourcesTreeItem.js
+++ b/devtools/client/debugger/src/components/PrimaryPanes/SourcesTreeItem.js
@@ -11,12 +11,14 @@ import { showMenu } from "devtools-contextmenu";
 
 import SourceIcon from "../shared/SourceIcon";
 import AccessibleImage from "../shared/AccessibleImage";
+import { getDisplayName, isWorker } from "../../utils/workers";
 
 import {
   getGeneratedSourceByURL,
   getHasSiblingOfSameName,
   hasPrettySource as checkHasPrettySource,
-  getContext
+  getContext,
+  getMainThread
 } from "../../selectors";
 import actions from "../../actions";
 
@@ -31,9 +33,10 @@ import { copyToTheClipboard } from "../../utils/clipboard";
 import { features } from "../../utils/prefs";
 
 import type { TreeNode } from "../../utils/sources-tree/types";
-import type { Source, Context } from "../../types";
+import type { Source, Context, MainThread, Thread } from "../../types";
 
 type Props = {
+  autoExpand: ?boolean,
   cx: Context,
   debuggeeUrl: string,
   projectRoot: string,
@@ -42,6 +45,8 @@ type Props = {
   depth: number,
   focused: boolean,
   expanded: boolean,
+  threads: Thread[],
+  mainThread: MainThread,
   hasMatchingGeneratedSource: boolean,
   hasSiblingOfSameName: boolean,
   hasPrettySource: boolean,
@@ -65,47 +70,17 @@ type MenuOption = {
 type ContextMenu = Array<MenuOption>;
 
 class SourceTreeItem extends Component<Props, State> {
-  getIcon(item: TreeNode, depth: number) {
-    const { debuggeeUrl, projectRoot, source, hasPrettySource } = this.props;
-
-    if (item.path === "webpack://") {
-      return <AccessibleImage className="webpack" />;
-    } else if (item.path === "ng://") {
-      return <AccessibleImage className="angular" />;
-    } else if (isUrlExtension(item.path) && depth === 0) {
-      return <AccessibleImage className="extension" />;
+  componentDidMount() {
+    const { autoExpand, item } = this.props;
+    if (autoExpand) {
+      this.props.setExpanded(item, true, false);
     }
-
-    if (depth === 0 && projectRoot === "") {
-      return (
-        <AccessibleImage
-          className={classnames("globe-small", {
-            debuggee: debuggeeUrl && debuggeeUrl.includes(item.name)
-          })}
-        />
-      );
-    }
-
-    if (isDirectory(item)) {
-      return <AccessibleImage className="folder" />;
-    }
-
-    if (hasPrettySource) {
-      return <AccessibleImage className="prettyPrint" />;
-    }
-
-    if (source) {
-      return <SourceIcon source={source} />;
-    }
-
-    return null;
   }
 
   onClick = (e: MouseEvent) => {
     const { item, focusItem, selectItem } = this.props;
 
     focusItem(item);
-
     if (!isDirectory(item)) {
       selectItem(item);
     }
@@ -208,8 +183,69 @@ class SourceTreeItem extends Component<Props, State> {
     );
   }
 
-  renderItemName() {
-    const { item } = this.props;
+  renderIcon(item: TreeNode, depth: number) {
+    const {
+      debuggeeUrl,
+      projectRoot,
+      source,
+      hasPrettySource,
+      threads
+    } = this.props;
+
+    if (item.name === "webpack://") {
+      return <AccessibleImage className="webpack" />;
+    } else if (item.name === "ng://") {
+      return <AccessibleImage className="angular" />;
+    } else if (isUrlExtension(item.path) && depth === 1) {
+      return <AccessibleImage className="extension" />;
+    }
+
+    // Threads level
+    if (depth === 0 && projectRoot === "") {
+      const thread = threads.find(thrd => thrd.actor == item.name);
+
+      if (thread) {
+        const icon = thread === this.props.mainThread ? "window" : "worker";
+        return (
+          <AccessibleImage
+            className={classnames(icon, {
+              debuggee: debuggeeUrl && debuggeeUrl.includes(item.name)
+            })}
+          />
+        );
+      }
+    }
+
+    if (isDirectory(item)) {
+      // Domain level
+      if (depth === 1) {
+        return <AccessibleImage className="globe-small" />;
+      }
+      return <AccessibleImage className="folder" />;
+    }
+
+    if (hasPrettySource) {
+      return <AccessibleImage className="prettyPrint" />;
+    }
+
+    if (source) {
+      return <SourceIcon source={source} />;
+    }
+
+    return null;
+  }
+
+  renderItemName(depth) {
+    const { item, threads } = this.props;
+
+    if (depth === 0) {
+      const thread = threads.find(({ actor }) => actor == item.name);
+      if (thread) {
+        return isWorker(thread)
+          ? getDisplayName((thread: any))
+          : L10N.getStr("mainThread");
+      }
+    }
 
     switch (item.name) {
       case "ng://":
@@ -253,10 +289,9 @@ class SourceTreeItem extends Component<Props, State> {
         onContextMenu={e => this.onContextMenu(e, item)}
       >
         {this.renderItemArrow()}
-        {this.getIcon(item, depth)}
+        {this.renderIcon(item, depth)}
         <span className="label">
-          {" "}
-          {this.renderItemName()}
+          {this.renderItemName(depth)}
           {query} {suffix}
         </span>
       </div>
@@ -276,6 +311,7 @@ const mapStateToProps = (state, props) => {
   const { source } = props;
   return {
     cx: getContext(state),
+    mainThread: getMainThread(state),
     hasMatchingGeneratedSource: getHasMatchingGeneratedSource(state, source),
     hasSiblingOfSameName: getHasSiblingOfSameName(state, source),
     hasPrettySource: source ? checkHasPrettySource(state, source.id) : false
diff --git a/devtools/client/debugger/src/components/PrimaryPanes/index.js b/devtools/client/debugger/src/components/PrimaryPanes/index.js
index 8046d7dc93ee..fd6c2374e4b7 100644
--- a/devtools/client/debugger/src/components/PrimaryPanes/index.js
+++ b/devtools/client/debugger/src/components/PrimaryPanes/index.js
@@ -127,9 +127,7 @@ class PrimaryPanes extends Component<Props, State> {
   }
 
   renderThreadSources() {
-    return this.props.threads.map(({ actor }) => (
-      <SourcesTree thread={actor} key={actor} />
-    ));
+    return <SourcesTree threads={this.props.threads} />;
   }
 
   render() {
diff --git a/devtools/client/debugger/src/components/PrimaryPanes/tests/SourcesTree.spec.js b/devtools/client/debugger/src/components/PrimaryPanes/tests/SourcesTree.spec.js
index 4492cd104ed3..64b1d102ba9e 100644
--- a/devtools/client/debugger/src/components/PrimaryPanes/tests/SourcesTree.spec.js
+++ b/devtools/client/debugger/src/components/PrimaryPanes/tests/SourcesTree.spec.js
@@ -83,8 +83,10 @@ describe("SourcesTree", () => {
         const newSource = createMockSource(
           "server1.conn13.child1/43",
           "http://mdn.com/four.js",
-          true
+          true,
+          ""
         );
+
         const newThreadSources = {
           ...props.sources.FakeThread,
           "server1.conn13.child1/43": newSource
@@ -92,15 +94,12 @@ describe("SourcesTree", () => {
 
         await component.setProps({
           ...props,
-          sources: {
-            ...props.sources,
-            ...newThreadSources
-          }
+          sources: newThreadSources
         });
 
         expect(
-          component.state("uncollapsedTree").contents[0].contents
-        ).toHaveLength(6);
+          component.state("uncollapsedTree").contents[0].contents[0].contents
+        ).toHaveLength(5);
       });
 
       it("updates sources if sources are emptied", async () => {
@@ -120,15 +119,17 @@ describe("SourcesTree", () => {
       it("recreates tree if projectRoot is changed", async () => {
         const { component, props, defaultState } = render();
         const sources = {
-          "server1.conn13.child1/41": createMockSource(
-            "server1.conn13.child1/41",
-            "http://mozilla.com/three.js"
-          )
+          FakeThread: {
+            "server1.conn13.child1/41": createMockSource(
+              "server1.conn13.child1/41",
+              "http://mozilla.com/three.js"
+            )
+          }
         };
 
-        expect(defaultState.uncollapsedTree.contents[0].contents).toHaveLength(
-          5
-        );
+        expect(
+          defaultState.uncollapsedTree.contents[0].contents[0].contents
+        ).toHaveLength(5);
 
         await component.setProps({
           ...props,
@@ -141,18 +142,22 @@ describe("SourcesTree", () => {
         ).toHaveLength(1);
       });
 
-      it("recreates tree if debugeeUrl is changed", async () => {
+      it("recreates tree if debuggeeUrl is changed", async () => {
         const { component, props, defaultState } = render();
         const sources = {
-          "server1.conn13.child1/41": createMockSource(
-            "server1.conn13.child1/41",
-            "http://mdn.com/three.js"
-          )
+          FakeThread: {
+            "server1.conn13.child1/41": createMockSource(
+              "server1.conn13.child1/41",
+              "http://mdn.com/three.js",
+              true,
+              ""
+            )
+          }
         };
 
-        expect(defaultState.uncollapsedTree.contents[0].contents).toHaveLength(
-          5
-        );
+        expect(
+          defaultState.uncollapsedTree.contents[0].contents[0].contents
+        ).toHaveLength(5);
 
         await component.setProps({
           ...props,
@@ -166,6 +171,56 @@ describe("SourcesTree", () => {
       });
     });
 
+    describe("updates threads", () => {
+      it("adds sources to the correct thread", async () => {
+        const { component, props } = render();
+        const newSource = createMockSource(
+          "server1.conn13.child1/43",
+          "http://mdn.com/four.js",
+          true,
+          ""
+        );
+
+        const newThreadSources = {
+          FakeThread1: {
+            "server1.conn13.child1/43": newSource
+          }
+        };
+
+        expect(component.state("uncollapsedTree").contents[0].name).toEqual(
+          "FakeThread"
+        );
+        expect(
+          component.state("uncollapsedTree").contents[0].contents[0].contents
+        ).toHaveLength(5);
+        expect(component.state("uncollapsedTree").contents[1]).toEqual(
+          undefined
+        );
+
+        await component.setProps({
+          ...props,
+          sources: {
+            ...props.sources,
+            ...newThreadSources
+          }
+        });
+
+        expect(component.state("uncollapsedTree").contents[0].name).toEqual(
+          "FakeThread"
+        );
+        expect(
+          component.state("uncollapsedTree").contents[0].contents[0].contents
+        ).toHaveLength(5);
+
+        expect(component.state("uncollapsedTree").contents[1].name).toEqual(
+          "FakeThread1"
+        );
+        expect(
+          component.state("uncollapsedTree").contents[1].contents[0].contents
+        ).toHaveLength(1);
+      });
+    });
+
     describe("updates highlighted items", () => {
       it("updates highlightItems if selectedSource changes", async () => {
         const { component, props } = render();
@@ -173,8 +228,7 @@ describe("SourcesTree", () => {
           "server1.conn13.child1/41",
           "http://mdn.com/three.js",
           false,
-          null,
-          "FakeThread"
+          null
         );
         await component.setProps({
           ...props,
@@ -247,10 +301,7 @@ describe("SourcesTree", () => {
         .find("ManagedTree")
         .props()
         .onExpand({}, expandedState);
-      expect(props.setExpandedState).toHaveBeenCalledWith(
-        "FakeThread",
-        expandedState
-      );
+      expect(props.setExpandedState).toHaveBeenCalledWith(expandedState);
     });
 
     it("onCollapse", async () => {
@@ -260,10 +311,7 @@ describe("SourcesTree", () => {
         .find("ManagedTree")
         .props()
         .onCollapse({}, expandedState);
-      expect(props.setExpandedState).toHaveBeenCalledWith(
-        "FakeThread",
-        expandedState
-      );
+      expect(props.setExpandedState).toHaveBeenCalledWith(expandedState);
     });
 
     it("getParent", async () => {
@@ -274,8 +322,8 @@ describe("SourcesTree", () => {
         .props()
         .getParent(item);
 
-      expect(parent.path).toEqual("mdn.com");
-      expect(parent.contents).toHaveLength(5);
+      expect(parent.path).toEqual("FakeThread");
+      expect(parent.contents[0].contents).toHaveLength(5);
     });
   });
 
@@ -283,31 +331,7 @@ describe("SourcesTree", () => {
     it("should return path for item", async () => {
       const { instance } = render();
       const path = instance.getPath(createMockItem());
-      expect(path).toEqual(
-        "http://mdn.com/one.js/one.js/server1.conn13.child1/39/"
-      );
-    });
-
-    it("should return path for blackboxedboxed item", async () => {
-      const item = createMockItem(
-        "http://mdn.com/blackboxed.js",
-        "blackboxed.js",
-        { id: "server1.conn13.child1/59" }
-      );
-
-      const sources = {
-        "server1.conn13.child1/59": createMockSource(
-          "server1.conn13.child1/59",
-          "http://mdn.com/blackboxed.js",
-          true
-        )
-      };
-
-      const { instance } = render({ sources });
-      const path = instance.getPath(item);
-      expect(path).toEqual(
-        "http://mdn.com/blackboxed.js/blackboxed.js/server1.conn13.child1/59/:blackboxed"
-      );
+      expect(path).toEqual("http://mdn.com/one.js/server1.conn13.child1/39/");
     });
 
     it("should return path for generated item", async () => {
@@ -318,7 +342,7 @@ describe("SourcesTree", () => {
         })
       );
       expect(pathOriginal).toEqual(
-        "http://mdn.com/four.js/four.js/server1.conn13.child1/42/originalSource-sha/"
+        "http://mdn.com/four.js/server1.conn13.child1/42/originalSource-sha/"
       );
 
       const pathGenerated = instance.getPath(
@@ -327,7 +351,7 @@ describe("SourcesTree", () => {
         })
       );
       expect(pathGenerated).toEqual(
-        "http://mdn.com/four.js/four.js/server1.conn13.child1/42/"
+        "http://mdn.com/four.js/server1.conn13.child1/42/"
       );
     });
   });
@@ -335,32 +359,42 @@ describe("SourcesTree", () => {
 
 function generateDefaults(overrides: Object) {
   const defaultSources = {
-    "server1.conn13.child1/39": createMockSource(
-      "server1.conn13.child1/39",
-      "http://mdn.com/one.js"
-    ),
-    "server1.conn13.child1/40": createMockSource(
-      "server1.conn13.child1/40",
-      "http://mdn.com/two.js"
-    ),
-    "server1.conn13.child1/41": createMockSource(
-      "server1.conn13.child1/41",
-      "http://mdn.com/three.js"
-    ),
-    "server1.conn13.child1/42/originalSource-sha": createMockSource(
-      "server1.conn13.child1/42/originalSource-sha",
-      "http://mdn.com/four.js"
-    ),
-    "server1.conn13.child1/42": createMockSource(
-      "server1.conn13.child1/42",
-      "http://mdn.com/four.js",
-      false,
-      "data:application/json?charset=utf?dsffewrsf"
-    )
+    FakeThread: {
+      "server1.conn13.child1/39": createMockSource(
+        "server1.conn13.child1/39",
+        "http://mdn.com/one.js",
+        false,
+        null
+      ),
+      "server1.conn13.child1/40": createMockSource(
+        "server1.conn13.child1/40",
+        "http://mdn.com/two.js",
+        false,
+        null
+      ),
+      "server1.conn13.child1/41": createMockSource(
+        "server1.conn13.child1/41",
+        "http://mdn.com/three.js",
+        false,
+        null
+      ),
+      "server1.conn13.child1/42/originalSource-sha": createMockSource(
+        "server1.conn13.child1/42/originalSource-sha",
+        "http://mdn.com/four.js",
+        false,
+        null
+      ),
+      "server1.conn13.child1/42": createMockSource(
+        "server1.conn13.child1/42",
+        "http://mdn.com/four.js",
+        false,
+        "data:application/json?charset=utf?dsffewrsf"
+      )
+    }
   };
+
   return {
     cx: mockcx,
-    thread: "FakeThread",
     autoExpandAll: true,
     selectSource: jest.fn(),
     setExpandedState: jest.fn(),
@@ -370,6 +404,16 @@ function generateDefaults(overrides: Object) {
     setProjectDirectoryRoot: jest.fn(),
     focusItem: jest.fn(),
     projectRoot: "",
+    threads: [
+      {
+        name: "FakeThread",
+        actor: "FakeThread"
+      },
+      {
+        name: "FakeThread1",
+        actor: "FakeThread1"
+      }
+    ],
     ...overrides
   };
 }
@@ -386,13 +430,7 @@ function render(overrides = {}) {
   return { component, props, defaultState, instance };
 }
 
-function createMockSource(
-  id,
-  url,
-  isBlackBoxed = false,
-  sourceMapURL = null,
-  thread = ""
-) {
+function createMockSource(id, url, isBlackBoxed = false, sourceMapURL = null) {
   return {
     ...makeMockSource(url, id),
     isBlackBoxed,
diff --git a/devtools/client/debugger/src/components/PrimaryPanes/tests/SourcesTreeItem.spec.js b/devtools/client/debugger/src/components/PrimaryPanes/tests/SourcesTreeItem.spec.js
index 88733a302315..15b0a527dc9b 100644
--- a/devtools/client/debugger/src/components/PrimaryPanes/tests/SourcesTreeItem.spec.js
+++ b/devtools/client/debugger/src/components/PrimaryPanes/tests/SourcesTreeItem.spec.js
@@ -375,6 +375,7 @@ function generateDefaults(overrides) {
     selectItem: jest.fn(),
     focusItem: jest.fn(),
     setExpanded: jest.fn(),
+    threads: [{ name: "Main Thread" }],
     ...overrides
   };
 }
@@ -389,7 +390,11 @@ function render(overrides = {}) {
   return { component, props, defaultState, instance };
 }
 
-function createMockDirectory(path = "folder/", name = "folder", contents = []) {
+function createMockDirectory(
+  path = "domain/subfolder",
+  name = "folder",
+  contents = []
+) {
   return {
     type: "directory",
     name,
diff --git a/devtools/client/debugger/src/components/PrimaryPanes/tests/__snapshots__/PrimaryPanes.spec.js.snap b/devtools/client/debugger/src/components/PrimaryPanes/tests/__snapshots__/PrimaryPanes.spec.js.snap
index aa905a73fda0..d07959bd25f9 100644
--- a/devtools/client/debugger/src/components/PrimaryPanes/tests/__snapshots__/PrimaryPanes.spec.js.snap
+++ b/devtools/client/debugger/src/components/PrimaryPanes/tests/__snapshots__/PrimaryPanes.spec.js.snap
@@ -57,6 +57,9 @@ exports[`PrimaryPanes with custom root renders custom root source list 1`] = `
           </span>
         </button>
       </div>
+      <Connect(SourcesTree)
+        threads={Array []}
+      />
     </div>
     <Connect(Outline)
       alphabetizeOutline={false}
@@ -123,6 +126,9 @@ exports[`PrimaryPanes with custom root renders empty custom root source list 1`]
           </span>
         </button>
       </div>
+      <Connect(SourcesTree)
+        threads={Array []}
+      />
     </div>
     <Connect(Outline)
       alphabetizeOutline={false}
diff --git a/devtools/client/debugger/src/components/PrimaryPanes/tests/__snapshots__/SourcesTree.spec.js.snap b/devtools/client/debugger/src/components/PrimaryPanes/tests/__snapshots__/SourcesTree.spec.js.snap
index 8a916b468d6e..2bee73f18f7f 100644
--- a/devtools/client/debugger/src/components/PrimaryPanes/tests/__snapshots__/SourcesTree.spec.js.snap
+++ b/devtools/client/debugger/src/components/PrimaryPanes/tests/__snapshots__/SourcesTree.spec.js.snap
@@ -2,29 +2,16 @@
 
 exports[`SourcesTree After changing expanded nodes Shows the tree with four.js, five.js and six.js expanded 1`] = `
 <div
-  className="sources-pane thread"
+  className="sources-pane"
   key="pane"
 >
-  <div
-    className="node thread-header"
-    key="thread-header"
-  >
-    <AccessibleImage
-      className="file"
-    />
-    <span
-      className="label"
-    >
-      Main Thread
-    </span>
-  </div>
   <div
     className="sources-list"
     key="tree"
   >
     <ManagedTree
       autoExpandAll={false}
-      autoExpandDepth={0}
+      autoExpandDepth={1}
       expanded={
         Array [
           "four.js",
@@ -51,22 +38,9 @@ exports[`SourcesTree After changing expanded nodes Shows the tree with four.js,
 
 exports[`SourcesTree Should show a 'No Sources' message if there are no sources 1`] = `
 <div
-  className="sources-pane thread"
+  className="sources-pane"
   key="pane"
 >
-  <div
-    className="node thread-header"
-    key="thread-header"
-  >
-    <AccessibleImage
-      className="file"
-    />
-    <span
-      className="label"
-    >
-      Main Thread
-    </span>
-  </div>
   <div
     className="no-sources-message"
     key="empty"
@@ -78,22 +52,9 @@ exports[`SourcesTree Should show a 'No Sources' message if there are no sources
 
 exports[`SourcesTree Should show the tree with nothing expanded 1`] = `
 <div
-  className="sources-pane thread"
+  className="sources-pane"
   key="pane"
 >
-  <div
-    className="node thread-header"
-    key="thread-header"
-  >
-    <AccessibleImage
-      className="file"
-    />
-    <span
-      className="label"
-    >
-      Main Thread
-    </span>
-  </div>
   <div
     className="sources-list"
     key="tree"
@@ -120,29 +81,16 @@ exports[`SourcesTree Should show the tree with nothing expanded 1`] = `
 
 exports[`SourcesTree When loading initial source Shows the tree with one.js, two.js and three.js expanded 1`] = `
 <div
-  className="sources-pane thread"
+  className="sources-pane"
   key="pane"
 >
-  <div
-    className="node thread-header"
-    key="thread-header"
-  >
-    <AccessibleImage
-      className="file"
-    />
-    <span
-      className="label"
-    >
-      Main Thread
-    </span>
-  </div>
   <div
     className="sources-list"
     key="tree"
   >
     <ManagedTree
       autoExpandAll={false}
-      autoExpandDepth={0}
+      autoExpandDepth={1}
       expanded={
         Array [
           "one.js",
@@ -169,22 +117,9 @@ exports[`SourcesTree When loading initial source Shows the tree with one.js, two
 
 exports[`SourcesTree on receiving new props updates highlighted items updates highlightItems if selectedSource changes 1`] = `
 <div
-  className="sources-pane thread"
+  className="sources-pane"
   key="pane"
 >
-  <div
-    className="node thread-header"
-    key="thread-header"
-  >
-    <AccessibleImage
-      className="file"
-    />
-    <span
-      className="label"
-    >
-      Main Thread
-    </span>
-  </div>
   <div
     className="sources-list"
     key="tree"
@@ -212,7 +147,7 @@ exports[`SourcesTree on receiving new props updates highlighted items updates hi
               "url": "http://mdn.com/three.js",
             },
             "name": "three.js",
-            "path": "mdn.com/three.js",
+            "path": "FakeThread/mdn.com/three.js",
             "type": "source",
           },
           Object {
@@ -231,7 +166,7 @@ exports[`SourcesTree on receiving new props updates highlighted items updates hi
                   "url": "http://mdn.com/four.js",
                 },
                 "name": "four.js",
-                "path": "mdn.com/four.js",
+                "path": "FakeThread/mdn.com/four.js",
                 "type": "source",
               },
               Object {
@@ -248,7 +183,7 @@ exports[`SourcesTree on receiving new props updates highlighted items updates hi
                   "url": "http://mdn.com/four.js",
                 },
                 "name": "four.js",
-                "path": "mdn.com/four.js",
+                "path": "FakeThread/mdn.com/four.js",
                 "type": "source",
               },
               Object {
@@ -265,7 +200,7 @@ exports[`SourcesTree on receiving new props updates highlighted items updates hi
                   "url": "http://mdn.com/one.js",
                 },
                 "name": "one.js",
-                "path": "mdn.com/one.js",
+                "path": "FakeThread/mdn.com/one.js",
                 "type": "source",
               },
               Object {
@@ -282,7 +217,7 @@ exports[`SourcesTree on receiving new props updates highlighted items updates hi
                   "url": "http://mdn.com/three.js",
                 },
                 "name": "three.js",
-                "path": "mdn.com/three.js",
+                "path": "FakeThread/mdn.com/three.js",
                 "type": "source",
               },
               Object {
@@ -299,12 +234,111 @@ exports[`SourcesTree on receiving new props updates highlighted items updates hi
                   "url": "http://mdn.com/two.js",
                 },
                 "name": "two.js",
-                "path": "mdn.com/two.js",
+                "path": "FakeThread/mdn.com/two.js",
                 "type": "source",
               },
             ],
             "name": "mdn.com",
-            "path": "mdn.com",
+            "path": "FakeThread/mdn.com",
+            "type": "directory",
+          },
+          Object {
+            "contents": Array [
+              Object {
+                "contents": Array [
+                  Object {
+                    "contents": Object {
+                      "id": "server1.conn13.child1/42",
+                      "introductionType": undefined,
+                      "introductionUrl": null,
+                      "isBlackBoxed": false,
+                      "isExtension": false,
+                      "isPrettyPrinted": false,
+                      "isWasm": false,
+                      "relativeUrl": "http://mdn.com/four.js",
+                      "sourceMapURL": "data:application/json?charset=utf?dsffewrsf",
+                      "url": "http://mdn.com/four.js",
+                    },
+                    "name": "four.js",
+                    "path": "FakeThread/mdn.com/four.js",
+                    "type": "source",
+                  },
+                  Object {
+                    "contents": Object {
+                      "id": "server1.conn13.child1/42/originalSource-sha",
+                      "introductionType": undefined,
+                      "introductionUrl": null,
+                      "isBlackBoxed": false,
+                      "isExtension": false,
+                      "isPrettyPrinted": false,
+                      "isWasm": false,
+                      "relativeUrl": "http://mdn.com/four.js",
+                      "sourceMapURL": null,
+                      "url": "http://mdn.com/four.js",
+                    },
+                    "name": "four.js",
+                    "path": "FakeThread/mdn.com/four.js",
+                    "type": "source",
+                  },
+                  Object {
+                    "contents": Object {
+                      "id": "server1.conn13.child1/39",
+                      "introductionType": undefined,
+                      "introductionUrl": null,
+                      "isBlackBoxed": false,
+                      "isExtension": false,
+                      "isPrettyPrinted": false,
+                      "isWasm": false,
+                      "relativeUrl": "http://mdn.com/one.js",
+                      "sourceMapURL": null,
+                      "url": "http://mdn.com/one.js",
+                    },
+                    "name": "one.js",
+                    "path": "FakeThread/mdn.com/one.js",
+                    "type": "source",
+                  },
+                  Object {
+                    "contents": Object {
+                      "id": "server1.conn13.child1/41",
+                      "introductionType": undefined,
+                      "introductionUrl": null,
+                      "isBlackBoxed": false,
+                      "isExtension": false,
+                      "isPrettyPrinted": false,
+                      "isWasm": false,
+                      "relativeUrl": "http://mdn.com/three.js",
+                      "sourceMapURL": null,
+                      "url": "http://mdn.com/three.js",
+                    },
+                    "name": "three.js",
+                    "path": "FakeThread/mdn.com/three.js",
+                    "type": "source",
+                  },
+                  Object {
+                    "contents": Object {
+                      "id": "server1.conn13.child1/40",
+                      "introductionType": undefined,
+                      "introductionUrl": null,
+                      "isBlackBoxed": false,
+                      "isExtension": false,
+                      "isPrettyPrinted": false,
+                      "isWasm": false,
+                      "relativeUrl": "http://mdn.com/two.js",
+                      "sourceMapURL": null,
+                      "url": "http://mdn.com/two.js",
+                    },
+                    "name": "two.js",
+                    "path": "FakeThread/mdn.com/two.js",
+                    "type": "source",
+                  },
+                ],
+                "name": "mdn.com",
+                "path": "FakeThread/mdn.com",
+                "type": "directory",
+              },
+            ],
+            "name": "FakeThread",
+            "path": "FakeThread",
             "type": "directory",
           },
         ]
diff --git a/devtools/client/debugger/src/components/PrimaryPanes/tests/__snapshots__/SourcesTreeItem.spec.js.snap b/devtools/client/debugger/src/components/PrimaryPanes/tests/__snapshots__/SourcesTreeItem.spec.js.snap
index 2d17ce7ed162..7d1fe01f965d 100644
--- a/devtools/client/debugger/src/components/PrimaryPanes/tests/__snapshots__/SourcesTreeItem.spec.js.snap
+++ b/devtools/client/debugger/src/components/PrimaryPanes/tests/__snapshots__/SourcesTreeItem.spec.js.snap
@@ -75,6 +75,11 @@ Object {
         "relativeUrl": "http://mdn.com/one.js",
         "url": "http://mdn.com/one.js",
       },
+      "threads": Array [
+        Object {
+          "name": "Main Thread",
+        },
+      ],
       "toggleBlackBox": [MockFunction],
     },
     "refs": Object {},
@@ -122,6 +127,13 @@ Object {
               "url": "http://mdn.com/one.js",
             }
           }
+          threads={
+            Array [
+              Object {
+                "name": "Main Thread",
+              },
+            ]
+          }
           toggleBlackBox={[MockFunction]}
         />,
         "_forcedUpdate": false,
@@ -198,6 +210,11 @@ Object {
       "relativeUrl": "http://mdn.com/one.js",
       "url": "http://mdn.com/one.js",
     },
+    "threads": Array [
+      Object {
+        "name": "Main Thread",
+      },
+    ],
     "toggleBlackBox": [MockFunction],
   },
 }
@@ -285,6 +302,11 @@ Object {
         "relativeUrl": "http://mdn.com/one.js",
         "url": "http://mdn.com/one.js",
       },
+      "threads": Array [
+        Object {
+          "name": "Main Thread",
+        },
+      ],
       "toggleBlackBox": [MockFunction],
     },
     "refs": Object {},
@@ -334,6 +356,13 @@ Object {
               "url": "http://mdn.com/one.js",
             }
           }
+          threads={
+            Array [
+              Object {
+                "name": "Main Thread",
+              },
+            ]
+          }
           toggleBlackBox={[MockFunction]}
         />,
         "_forcedUpdate": false,
@@ -417,6 +446,11 @@ Object {
       "relativeUrl": "http://mdn.com/one.js",
       "url": "http://mdn.com/one.js",
     },
+    "threads": Array [
+      Object {
+        "name": "Main Thread",
+      },
+    ],
     "toggleBlackBox": [MockFunction],
   },
 }
@@ -433,8 +467,20 @@ Object {
     <span
       className="img no-arrow"
     />
-    <AccessibleImage
-      className="globe-small"
+    <Connect(SourceIcon)
+      source={
+        Object {
+          "id": "server1.conn13.child1/39",
+          "introductionType": undefined,
+          "introductionUrl": null,
+          "isBlackBoxed": false,
+          "isExtension": false,
+          "isPrettyPrinted": false,
+          "isWasm": false,
+          "relativeUrl": "http://mdn.com/one.js",
+          "url": "http://mdn.com/one.js",
+        }
+      }
     />
     <span
       className="label"
@@ -487,6 +533,11 @@ Object {
         "relativeUrl": "http://mdn.com/one.js",
         "url": "http://mdn.com/one.js",
       },
+      "threads": Array [
+        Object {
+          "name": "Main Thread",
+        },
+      ],
       "toggleBlackBox": [MockFunction],
     },
     "refs": Object {},
@@ -536,6 +587,13 @@ Object {
               "url": "http://mdn.com/one.js",
             }
           }
+          threads={
+            Array [
+              Object {
+                "name": "Main Thread",
+              },
+            ]
+          }
           toggleBlackBox={[MockFunction]}
         />,
         "_forcedUpdate": false,
@@ -549,8 +607,20 @@ Object {
           <span
             className="img no-arrow"
           />
-          <AccessibleImage
-            className="globe-small"
+          <Connect(SourceIcon)
+            source={
+              Object {
+                "id": "server1.conn13.child1/39",
+                "introductionType": undefined,
+                "introductionUrl": null,
+                "isBlackBoxed": false,
+                "isExtension": false,
+                "isPrettyPrinted": false,
+                "isWasm": false,
+                "relativeUrl": "http://mdn.com/one.js",
+                "url": "http://mdn.com/one.js",
+              }
+            }
           />
           <span
             className="label"
@@ -602,6 +672,11 @@ Object {
       "relativeUrl": "http://mdn.com/one.js",
       "url": "http://mdn.com/one.js",
     },
+    "threads": Array [
+      Object {
+        "name": "Main Thread",
+      },
+    ],
     "toggleBlackBox": [MockFunction],
   },
 }
@@ -619,7 +694,7 @@ Object {
       className="arrow"
     />
     <AccessibleImage
-      className="globe-small debuggee"
+      className="folder"
     />
     <span
       className="label"
@@ -662,6 +737,11 @@ Object {
         "relativeUrl": "http://mdn.com/one.js",
         "url": "http://mdn.com/one.js",
       },
+      "threads": Array [
+        Object {
+          "name": "Main Thread",
+        },
+      ],
       "toggleBlackBox": [MockFunction],
     },
     "refs": Object {},
@@ -701,6 +781,13 @@ Object {
               "url": "http://mdn.com/one.js",
             }
           }
+          threads={
+            Array [
+              Object {
+                "name": "Main Thread",
+              },
+            ]
+          }
           toggleBlackBox={[MockFunction]}
         />,
         "_forcedUpdate": false,
@@ -715,7 +802,7 @@ Object {
             className="arrow"
           />
           <AccessibleImage
-            className="globe-small debuggee"
+            className="folder"
           />
           <span
             className="label"
@@ -757,6 +844,11 @@ Object {
       "relativeUrl": "http://mdn.com/one.js",
       "url": "http://mdn.com/one.js",
     },
+    "threads": Array [
+      Object {
+        "name": "Main Thread",
+      },
+    ],
     "toggleBlackBox": [MockFunction],
   },
 }
@@ -774,7 +866,7 @@ Object {
       className="arrow"
     />
     <AccessibleImage
-      className="globe-small debuggee"
+      className="folder"
     />
     <span
       className="label"
@@ -818,6 +910,11 @@ Object {
         "relativeUrl": "http://mdn.com/one.js",
         "url": "http://mdn.com/one.js",
       },
+      "threads": Array [
+        Object {
+          "name": "Main Thread",
+        },
+      ],
       "toggleBlackBox": [MockFunction],
     },
     "refs": Object {},
@@ -858,6 +955,13 @@ Object {
               "url": "http://mdn.com/one.js",
             }
           }
+          threads={
+            Array [
+              Object {
+                "name": "Main Thread",
+              },
+            ]
+          }
           toggleBlackBox={[MockFunction]}
         />,
         "_forcedUpdate": false,
@@ -872,7 +976,7 @@ Object {
             className="arrow"
           />
           <AccessibleImage
-            className="globe-small debuggee"
+            className="folder"
           />
           <span
             className="label"
@@ -915,6 +1019,11 @@ Object {
       "relativeUrl": "http://mdn.com/one.js",
       "url": "http://mdn.com/one.js",
     },
+    "threads": Array [
+      Object {
+        "name": "Main Thread",
+      },
+    ],
     "toggleBlackBox": [MockFunction],
   },
 }
@@ -924,7 +1033,7 @@ exports[`SourceTreeItem renderItem should show focused item for folder with expa
 Object {
   "component": <div
     className="node focused"
-    key="folder/"
+    key="domain/subfolder"
     onClick={[Function]}
     onContextMenu={[Function]}
   >
@@ -932,7 +1041,7 @@ Object {
       className="arrow expanded"
     />
     <AccessibleImage
-      className="folder"
+      className="globe-small"
     />
     <span
       className="label"
@@ -958,7 +1067,7 @@ Object {
       "item": Object {
         "contents": Array [],
         "name": "folder",
-        "path": "folder/",
+        "path": "domain/subfolder",
         "type": "directory",
       },
       "projectRoot": "",
@@ -966,6 +1075,11 @@ Object {
       "setExpanded": [MockFunction],
       "setProjectDirectoryRoot": [MockFunction],
       "source": null,
+      "threads": Array [
+        Object {
+          "name": "Main Thread",
+        },
+      ],
       "toggleBlackBox": [MockFunction],
     },
     "refs": Object {},
@@ -985,7 +1099,7 @@ Object {
             Object {
               "contents": Array [],
               "name": "folder",
-              "path": "folder/",
+              "path": "domain/subfolder",
               "type": "directory",
             }
           }
@@ -994,6 +1108,13 @@ Object {
           setExpanded={[MockFunction]}
           setProjectDirectoryRoot={[MockFunction]}
           source={null}
+          threads={
+            Array [
+              Object {
+                "name": "Main Thread",
+              },
+            ]
+          }
           toggleBlackBox={[MockFunction]}
         />,
         "_forcedUpdate": false,
@@ -1008,7 +1129,7 @@ Object {
             className="arrow expanded"
           />
           <AccessibleImage
-            className="folder"
+            className="globe-small"
           />
           <span
             className="label"
@@ -1033,7 +1154,7 @@ Object {
     "item": Object {
       "contents": Array [],
       "name": "folder",
-      "path": "folder/",
+      "path": "domain/subfolder",
       "type": "directory",
     },
     "projectRoot": "",
@@ -1041,6 +1162,11 @@ Object {
     "setExpanded": [MockFunction],
     "setProjectDirectoryRoot": [MockFunction],
     "source": null,
+    "threads": Array [
+      Object {
+        "name": "Main Thread",
+      },
+    ],
     "toggleBlackBox": [MockFunction],
   },
 }
@@ -1100,6 +1226,11 @@ Object {
         "relativeUrl": "http://mdn.com/one.js",
         "url": "http://mdn.com/one.js",
       },
+      "threads": Array [
+        Object {
+          "name": "Main Thread",
+        },
+      ],
       "toggleBlackBox": [MockFunction],
     },
     "refs": Object {},
@@ -1138,6 +1269,13 @@ Object {
               "url": "http://mdn.com/one.js",
             }
           }
+          threads={
+            Array [
+              Object {
+                "name": "Main Thread",
+              },
+            ]
+          }
           toggleBlackBox={[MockFunction]}
         />,
         "_forcedUpdate": false,
@@ -1193,6 +1331,11 @@ Object {
       "relativeUrl": "http://mdn.com/one.js",
       "url": "http://mdn.com/one.js",
     },
+    "threads": Array [
+      Object {
+        "name": "Main Thread",
+      },
+    ],
     "toggleBlackBox": [MockFunction],
   },
 }
@@ -1202,7 +1345,7 @@ exports[`SourceTreeItem renderItem should show icon for folder with arrow 1`] =
 Object {
   "component": <div
     className="node"
-    key="folder/"
+    key="domain/subfolder"
     onClick={[Function]}
     onContextMenu={[Function]}
   >
@@ -1234,7 +1377,7 @@ Object {
       "item": Object {
         "contents": Array [],
         "name": "folder",
-        "path": "folder/",
+        "path": "domain/subfolder",
         "type": "directory",
       },
       "projectRoot": "",
@@ -1242,6 +1385,11 @@ Object {
       "setExpanded": [MockFunction],
       "setProjectDirectoryRoot": [MockFunction],
       "source": null,
+      "threads": Array [
+        Object {
+          "name": "Main Thread",
+        },
+      ],
       "toggleBlackBox": [MockFunction],
     },
     "refs": Object {},
@@ -1259,7 +1407,7 @@ Object {
             Object {
               "contents": Array [],
               "name": "folder",
-              "path": "folder/",
+              "path": "domain/subfolder",
               "type": "directory",
             }
           }
@@ -1268,6 +1416,13 @@ Object {
           setExpanded={[MockFunction]}
           setProjectDirectoryRoot={[MockFunction]}
           source={null}
+          threads={
+            Array [
+              Object {
+                "name": "Main Thread",
+              },
+            ]
+          }
           toggleBlackBox={[MockFunction]}
         />,
         "_forcedUpdate": false,
@@ -1305,7 +1460,7 @@ Object {
     "item": Object {
       "contents": Array [],
       "name": "folder",
-      "path": "folder/",
+      "path": "domain/subfolder",
       "type": "directory",
     },
     "projectRoot": "",
@@ -1313,6 +1468,11 @@ Object {
     "setExpanded": [MockFunction],
     "setProjectDirectoryRoot": [MockFunction],
     "source": null,
+    "threads": Array [
+      Object {
+        "name": "Main Thread",
+      },
+    ],
     "toggleBlackBox": [MockFunction],
   },
 }
@@ -1322,7 +1482,7 @@ exports[`SourceTreeItem renderItem should show icon for folder with expanded arr
 Object {
   "component": <div
     className="node"
-    key="folder/"
+    key="domain/subfolder"
     onClick={[Function]}
     onContextMenu={[Function]}
   >
@@ -1330,7 +1490,7 @@ Object {
       className="arrow expanded"
     />
     <AccessibleImage
-      className="folder"
+      className="globe-small"
     />
     <span
       className="label"
@@ -1356,7 +1516,7 @@ Object {
       "item": Object {
         "contents": Array [],
         "name": "folder",
-        "path": "folder/",
+        "path": "domain/subfolder",
         "type": "directory",
       },
       "projectRoot": "",
@@ -1364,6 +1524,11 @@ Object {
       "setExpanded": [MockFunction],
       "setProjectDirectoryRoot": [MockFunction],
       "source": null,
+      "threads": Array [
+        Object {
+          "name": "Main Thread",
+        },
+      ],
       "toggleBlackBox": [MockFunction],
     },
     "refs": Object {},
@@ -1383,7 +1548,7 @@ Object {
             Object {
               "contents": Array [],
               "name": "folder",
-              "path": "folder/",
+              "path": "domain/subfolder",
               "type": "directory",
             }
           }
@@ -1392,6 +1557,13 @@ Object {
           setExpanded={[MockFunction]}
           setProjectDirectoryRoot={[MockFunction]}
           source={null}
+          threads={
+            Array [
+              Object {
+                "name": "Main Thread",
+              },
+            ]
+          }
           toggleBlackBox={[MockFunction]}
         />,
         "_forcedUpdate": false,
@@ -1406,7 +1578,7 @@ Object {
             className="arrow expanded"
           />
           <AccessibleImage
-            className="folder"
+            className="globe-small"
           />
           <span
             className="label"
@@ -1431,7 +1603,7 @@ Object {
     "item": Object {
       "contents": Array [],
       "name": "folder",
-      "path": "folder/",
+      "path": "domain/subfolder",
       "type": "directory",
     },
     "projectRoot": "",
@@ -1439,6 +1611,11 @@ Object {
     "setExpanded": [MockFunction],
     "setProjectDirectoryRoot": [MockFunction],
     "source": null,
+    "threads": Array [
+      Object {
+        "name": "Main Thread",
+      },
+    ],
     "toggleBlackBox": [MockFunction],
   },
 }
@@ -1456,7 +1633,7 @@ Object {
       className="arrow"
     />
     <AccessibleImage
-      className="extension"
+      className="folder"
     />
     <span
       className="label"
@@ -1499,6 +1676,11 @@ Object {
         "relativeUrl": "http://mdn.com/one.js",
         "url": "http://mdn.com/one.js",
       },
+      "threads": Array [
+        Object {
+          "name": "Main Thread",
+        },
+      ],
       "toggleBlackBox": [MockFunction],
     },
     "refs": Object {},
@@ -1538,6 +1720,13 @@ Object {
               "url": "http://mdn.com/one.js",
             }
           }
+          threads={
+            Array [
+              Object {
+                "name": "Main Thread",
+              },
+            ]
+          }
           toggleBlackBox={[MockFunction]}
         />,
         "_forcedUpdate": false,
@@ -1552,7 +1741,7 @@ Object {
             className="arrow"
           />
           <AccessibleImage
-            className="extension"
+            className="folder"
           />
           <span
             className="label"
@@ -1594,6 +1783,11 @@ Object {
       "relativeUrl": "http://mdn.com/one.js",
       "url": "http://mdn.com/one.js",
     },
+    "threads": Array [
+      Object {
+        "name": "Main Thread",
+      },
+    ],
     "toggleBlackBox": [MockFunction],
   },
 }
@@ -1653,6 +1847,11 @@ Object {
         "relativeUrl": "http://mdn.com/one.js",
         "url": "http://mdn.com/one.js",
       },
+      "threads": Array [
+        Object {
+          "name": "Main Thread",
+        },
+      ],
       "toggleBlackBox": [MockFunction],
     },
     "refs": Object {},
@@ -1691,6 +1890,13 @@ Object {
               "url": "http://mdn.com/one.js",
             }
           }
+          threads={
+            Array [
+              Object {
+                "name": "Main Thread",
+              },
+            ]
+          }
           toggleBlackBox={[MockFunction]}
         />,
         "_forcedUpdate": false,
@@ -1746,6 +1952,11 @@ Object {
       "relativeUrl": "http://mdn.com/one.js",
       "url": "http://mdn.com/one.js",
     },
+    "threads": Array [
+      Object {
+        "name": "Main Thread",
+      },
+    ],
     "toggleBlackBox": [MockFunction],
   },
 }
@@ -1827,6 +2038,11 @@ Object {
         "relativeUrl": "http://mdn.com/one.js",
         "url": "http://mdn.com/one.js",
       },
+      "threads": Array [
+        Object {
+          "name": "Main Thread",
+        },
+      ],
       "toggleBlackBox": [MockFunction],
     },
     "refs": Object {},
@@ -1875,6 +2091,13 @@ Object {
               "url": "http://mdn.com/one.js",
             }
           }
+          threads={
+            Array [
+              Object {
+                "name": "Main Thread",
+              },
+            ]
+          }
           toggleBlackBox={[MockFunction]}
         />,
         "_forcedUpdate": false,
@@ -1952,6 +2175,11 @@ Object {
       "relativeUrl": "http://mdn.com/one.js",
       "url": "http://mdn.com/one.js",
     },
+    "threads": Array [
+      Object {
+        "name": "Main Thread",
+      },
+    ],
     "toggleBlackBox": [MockFunction],
   },
 }
@@ -2034,6 +2262,11 @@ Object {
         "relativeUrl": "http://mdn.com/one.js",
         "url": "http://mdn.com/one.js",
       },
+      "threads": Array [
+        Object {
+          "name": "Main Thread",
+        },
+      ],
       "toggleBlackBox": [MockFunction],
     },
     "refs": Object {},
@@ -2083,6 +2316,13 @@ Object {
               "url": "http://mdn.com/one.js",
             }
           }
+          threads={
+            Array [
+              Object {
+                "name": "Main Thread",
+              },
+            ]
+          }
           toggleBlackBox={[MockFunction]}
         />,
         "_forcedUpdate": false,
@@ -2161,6 +2401,11 @@ Object {
       "relativeUrl": "http://mdn.com/one.js",
       "url": "http://mdn.com/one.js",
     },
+    "threads": Array [
+      Object {
+        "name": "Main Thread",
+      },
+    ],
     "toggleBlackBox": [MockFunction],
   },
 }
@@ -2242,6 +2487,11 @@ Object {
         "relativeUrl": "http://mdn.com/one.js",
         "url": "http://mdn.com/one.js",
       },
+      "threads": Array [
+        Object {
+          "name": "Main Thread",
+        },
+      ],
       "toggleBlackBox": [MockFunction],
     },
     "refs": Object {},
@@ -2290,6 +2540,13 @@ Object {
               "url": "http://mdn.com/one.js",
             }
           }
+          threads={
+            Array [
+              Object {
+                "name": "Main Thread",
+              },
+            ]
+          }
           toggleBlackBox={[MockFunction]}
         />,
         "_forcedUpdate": false,
@@ -2367,6 +2624,11 @@ Object {
       "relativeUrl": "http://mdn.com/one.js",
       "url": "http://mdn.com/one.js",
     },
+    "threads": Array [
+      Object {
+        "name": "Main Thread",
+      },
+    ],
     "toggleBlackBox": [MockFunction],
   },
 }
diff --git a/devtools/client/debugger/src/components/QuickOpenModal.js b/devtools/client/debugger/src/components/QuickOpenModal.js
index 76501100a2d5..bd98b9e59c06 100644
--- a/devtools/client/debugger/src/components/QuickOpenModal.js
+++ b/devtools/client/debugger/src/components/QuickOpenModal.js
@@ -430,11 +430,12 @@ export class QuickOpenModal extends Component<Props, State> {
 /* istanbul ignore next: ignoring testing of redux connection stuff */
 function mapStateToProps(state) {
   const selectedSource = getSelectedSource(state);
+  const displayedSources = getDisplayedSourcesList(state);
 
   return {
     cx: getContext(state),
     enabled: getQuickOpenEnabled(state),
-    sources: formatSources(getDisplayedSourcesList(state), getTabs(state)),
+    sources: formatSources(displayedSources, getTabs(state)),
     selectedSource,
     selectedContentLoaded: selectedSource
       ? !!getSourceContent(state, selectedSource.id)
diff --git a/devtools/client/debugger/src/components/SecondaryPanes/Worker.js b/devtools/client/debugger/src/components/SecondaryPanes/Worker.js
index 3910c821804b..397e46b48931 100644
--- a/devtools/client/debugger/src/components/SecondaryPanes/Worker.js
+++ b/devtools/client/debugger/src/components/SecondaryPanes/Worker.js
@@ -44,7 +44,7 @@ export class Worker extends Component<Props> {
         onClick={this.onSelectThread}
       >
         <div className="icon">
-          <AccessibleImage className={worker ? "worker" : "file"} />
+          <AccessibleImage className={worker ? "worker" : "window"} />
         </div>
         <div className="label">{label}</div>
         {isPaused ? (
diff --git a/devtools/client/debugger/src/components/shared/AccessibleImage.css b/devtools/client/debugger/src/components/shared/AccessibleImage.css
index 308f238c7114..c463f3b57e8e 100644
--- a/devtools/client/debugger/src/components/shared/AccessibleImage.css
+++ b/devtools/client/debugger/src/components/shared/AccessibleImage.css
@@ -80,6 +80,11 @@ html[dir="rtl"] .img.arrow {
   mask-size: 12px 12px;
 }
 
+.img.window {
+  mask-image: url(resource://devtools/client/debugger/images/window.svg);
+  mask-size: 12px 12px;
+}
+
 .img.file {
   mask-image: url(resource://devtools/client/debugger/images/file-small.svg);
   mask-size: 12px 12px;
diff --git a/devtools/client/debugger/src/reducers/debuggee.js b/devtools/client/debugger/src/reducers/debuggee.js
index f3df260a662c..110ee943a147 100644
--- a/devtools/client/debugger/src/reducers/debuggee.js
+++ b/devtools/client/debugger/src/reducers/debuggee.js
@@ -10,9 +10,12 @@
  */
 
 import { sortBy } from "lodash";
+import { createSelector } from "reselect";
+
 import { getDisplayName } from "../utils/workers";
 
-import type { MainThread, WorkerList } from "../types";
+import type { Selector } from "./types";
+import type { MainThread, WorkerList, Thread } from "../types";
 import type { Action } from "../actions/types";
 
 export type DebuggeeState = {
@@ -21,7 +24,10 @@ export type DebuggeeState = {
 };
 
 export function initialDebuggeeState(): DebuggeeState {
-  return { workers: [], mainThread: { actor: "", url: "", type: -1 } };
+  return {
+    workers: [],
+    mainThread: { actor: "", url: "", type: -1, name: "" }
+  };
 }
 
 export default function debuggee(
@@ -32,13 +38,10 @@ export default function debuggee(
     case "CONNECT":
       return {
         ...state,
-        mainThread: action.mainThread
+        mainThread: { ...action.mainThread, name: L10N.getStr("mainThread") }
       };
     case "INSERT_WORKERS":
-      return {
-        ...state,
-        workers: [...state.workers, ...action.workers]
-      };
+      return insertWorkers(state, action.workers);
     case "REMOVE_WORKERS":
       const { workers } = action;
       return {
@@ -55,6 +58,18 @@ export default function debuggee(
   }
 }
 
+function insertWorkers(state, workers) {
+  const formatedWorkers = workers.map(worker => ({
+    ...worker,
+    name: getDisplayName(worker)
+  }));
+
+  return {
+    ...state,
+    workers: [...state.workers, ...formatedWorkers]
+  };
+}
+
 export const getWorkers = (state: OuterState) => state.debuggee.workers;
 
 export const getWorkerCount = (state: OuterState) => getWorkers(state).length;
@@ -71,8 +86,10 @@ export function getDebuggeeUrl(state: OuterState): string {
   return getMainThread(state).url;
 }
 
-export function getThreads(state: OuterState) {
-  return [getMainThread(state), ...sortBy(getWorkers(state), getDisplayName)];
-}
+export const getThreads: Selector<Thread[]> = createSelector(
+  getMainThread,
+  getWorkers,
+  (mainThread, workers) => [mainThread, ...sortBy(workers, getDisplayName)]
+);
 
 type OuterState = { debuggee: DebuggeeState };
diff --git a/devtools/client/debugger/src/reducers/source-tree.js b/devtools/client/debugger/src/reducers/source-tree.js
index 764df5fa2d90..4a0f69e3e0e4 100644
--- a/devtools/client/debugger/src/reducers/source-tree.js
+++ b/devtools/client/debugger/src/reducers/source-tree.js
@@ -9,15 +9,17 @@
  * @module reducers/source-tree
  */
 
-import type { SourceTreeAction } from "../actions/types";
+import type { SourceTreeAction, FocusItem } from "../actions/types";
 
 export type SourceTreeState = {
-  expanded: { [string]: Set<string> }
+  expanded: Set<string>,
+  focusedItem: ?FocusItem
 };
 
 export function InitialState(): SourceTreeState {
   return {
-    expanded: {}
+    expanded: new Set(),
+    focusedItem: null
   };
 }
 
@@ -28,6 +30,9 @@ export default function update(
   switch (action.type) {
     case "SET_EXPANDED_STATE":
       return updateExpanded(state, action);
+
+    case "SET_FOCUSED_SOURCE_ITEM":
+      return { ...state, focusedItem: action.item };
   }
 
   return state;
@@ -36,7 +41,7 @@ export default function update(
 function updateExpanded(state, action) {
   return {
     ...state,
-    expanded: { ...state.expanded, [action.thread]: new Set(action.expanded) }
+    expanded: new Set(action.expanded)
   };
 }
 
@@ -44,6 +49,10 @@ type OuterState = {
   sourceTree: SourceTreeState
 };
 
-export function getExpandedState(state: OuterState, thread: string) {
-  return state.sourceTree.expanded[thread];
+export function getExpandedState(state: OuterState) {
+  return state.sourceTree.expanded;
+}
+
+export function getFocusedSourceItem(state: OuterState): ?FocusItem {
+  return state.sourceTree.focusedItem;
 }
diff --git a/devtools/client/debugger/src/reducers/sources.js b/devtools/client/debugger/src/reducers/sources.js
index 2b6d1301aa27..fecc8a729373 100644
--- a/devtools/client/debugger/src/reducers/sources.js
+++ b/devtools/client/debugger/src/reducers/sources.js
@@ -68,8 +68,9 @@ export type SourcesMap = { [SourceId]: Source };
 type SourcesContentMap = {
   [SourceId]: AsyncValue<SourceContent> | null
 };
-export type BreakpointPositionsMap = { [SourceId]: BreakpointPositions };
 export type SourcesMapByThread = { [ThreadId]: SourcesMap };
+
+export type BreakpointPositionsMap = { [SourceId]: BreakpointPositions };
 type SourceActorMap = { [SourceId]: Array<SourceActorId> };
 
 type UrlsMap = { [string]: SourceId[] };
@@ -852,9 +853,10 @@ const getDisplayedSourceIDs: GetDisplayedSourceIDsSelector = createSelector(
     return sourceIDsByThread;
   }
 );
+
 type GetDisplayedSourcesSelector = (
   OuterState & SourceActorOuterState
-) => { [ThreadId]: { [SourceId]: Source } };
+) => SourcesMapByThread;
 export const getDisplayedSources: GetDisplayedSourcesSelector = createSelector(
   state => state.sources.sources,
   getDisplayedSourceIDs,
@@ -874,17 +876,6 @@ export const getDisplayedSources: GetDisplayedSourcesSelector = createSelector(
   }
 );
 
-export function getDisplayedSourcesForThread(
-  state: OuterState & SourceActorOuterState,
-  thread: string
-): SourcesMap {
-  return getDisplayedSources(state)[thread] || {};
-}
-
-export function getFocusedSourceItem(state: OuterState): ?FocusItem {
-  return state.sources.focusedItem;
-}
-
 export function getSourceActorsForSource(
   state: OuterState & SourceActorOuterState,
   id: SourceId
diff --git a/devtools/client/debugger/src/reducers/tests/sources.spec.js b/devtools/client/debugger/src/reducers/tests/sources.spec.js
index 92f44c96c4ab..7a03fe96344b 100644
--- a/devtools/client/debugger/src/reducers/tests/sources.spec.js
+++ b/devtools/client/debugger/src/reducers/tests/sources.spec.js
@@ -81,7 +81,6 @@ describe("sources selectors", () => {
       sources: update(state, {
         type: "ADD_SOURCES",
         cx: mockcx,
-        // coercing to a Source for the purpose of this test
         sources: ((mockedSources: any): Source[])
       }),
       sourceActors: undefined
@@ -94,9 +93,8 @@ describe("sources selectors", () => {
       sources: update(state.sources, insertAction),
       sourceActors: updateSourceActors(state.sourceActors, insertAction)
     };
-    const selectedDisplayedSources = getDisplayedSources(state);
-    const threadSources = selectedDisplayedSources.foo;
-    expect(Object.values(threadSources)).toHaveLength(3);
+    const threadSources = getDisplayedSources(state);
+    expect(Object.values(threadSources.foo)).toHaveLength(3);
   });
 
   it("should omit all extensions when chrome preference enabled", () => {
@@ -106,7 +104,6 @@ describe("sources selectors", () => {
       sources: update(state, {
         type: "ADD_SOURCES",
         cx: mockcx,
-        // coercing to a Source for the purpose of this test
         sources: ((mockedSources: any): Source[])
       }),
       sourceActors: undefined
@@ -121,8 +118,7 @@ describe("sources selectors", () => {
       sources: update(state.sources, insertAction),
       sourceActors: updateSourceActors(state.sourceActors, insertAction)
     };
-    const selectedDisplayedSources = getDisplayedSources(state);
-    const threadSources = selectedDisplayedSources.foo;
-    expect(Object.values(threadSources)).toHaveLength(1);
+    const threadSources = getDisplayedSources(state);
+    expect(Object.values(threadSources.foo)).toHaveLength(1);
   });
 });
diff --git a/devtools/client/debugger/src/types.js b/devtools/client/debugger/src/types.js
index 8c1da9d8fa5a..7e8bda074087 100644
--- a/devtools/client/debugger/src/types.js
+++ b/devtools/client/debugger/src/types.js
@@ -447,13 +447,15 @@ export type Scope = {|
 export type MainThread = {
   +actor: ThreadId,
   +url: string,
-  +type: number
+  +type: number,
+  +name: string
 };
 
 export type Worker = {
   +actor: ThreadId,
   +url: string,
-  +type: number
+  +type: number,
+  +name: string
 };
 
 export type Thread = MainThread & Worker;
diff --git a/devtools/client/debugger/src/utils/source.js b/devtools/client/debugger/src/utils/source.js
index 8c2298d2ed72..bd89b7db6c4d 100644
--- a/devtools/client/debugger/src/utils/source.js
+++ b/devtools/client/debugger/src/utils/source.js
@@ -491,7 +491,7 @@ export function getSourceQueryString(source: ?Source) {
 }
 
 export function isUrlExtension(url: string) {
-  return /^(chrome|moz)-extension:\//.test(url);
+  return /\/?(chrome|moz)-extension:\//.test(url);
 }
 
 export function getPlainUrl(url: string): string {
diff --git a/devtools/client/debugger/src/utils/sources-tree/addToTree.js b/devtools/client/debugger/src/utils/sources-tree/addToTree.js
index d4c01a67bad2..a9c2ff037c37 100644
--- a/devtools/client/debugger/src/utils/sources-tree/addToTree.js
+++ b/devtools/client/debugger/src/utils/sources-tree/addToTree.js
@@ -90,15 +90,25 @@ function traverseTree(
   url: ParsedURL,
   tree: TreeDirectory,
   debuggeeHost: ?string,
-  source: Source
+  source: Source,
+  thread: string
 ): TreeNode {
   const parts = url.path.split("/").filter(p => p !== "");
   parts.unshift(url.group);
+  if (thread) {
+    parts.unshift(thread);
+  }
 
   let path = "";
   return parts.reduce((subTree, part, index) => {
-    path = path ? `${path}/${part}` : part;
-    const debuggeeHostIfRoot = index === 0 ? debuggeeHost : null;
+    if (index == 0 && thread) {
+      path = thread;
+    } else {
+      path = `${path}/${part}`;
+    }
+
+    const debuggeeHostIfRoot = index === 1 ? debuggeeHost : null;
+
     return findOrCreateNode(
       parts,
       subTree,
@@ -165,7 +175,8 @@ function addSourceToNode(
 export function addToTree(
   tree: TreeDirectory,
   source: Source,
-  debuggeeHost: ?string
+  debuggeeHost: ?string,
+  thread: string
 ) {
   const url = getURL(source, debuggeeHost);
 
@@ -173,7 +184,7 @@ export function addToTree(
     return;
   }
 
-  const finalNode = traverseTree(url, tree, debuggeeHost, source);
+  const finalNode = traverseTree(url, tree, debuggeeHost, source, thread);
 
   // $FlowIgnore
   finalNode.contents = addSourceToNode(finalNode, url, source);
diff --git a/devtools/client/debugger/src/utils/sources-tree/collapseTree.js b/devtools/client/debugger/src/utils/sources-tree/collapseTree.js
index 4ff81613267e..57d3e898496d 100644
--- a/devtools/client/debugger/src/utils/sources-tree/collapseTree.js
+++ b/devtools/client/debugger/src/utils/sources-tree/collapseTree.js
@@ -18,8 +18,9 @@ function _collapseTree(node: TreeNode, depth: number): TreeNode {
       console.log(`Expected array at: ${node.path}`);
     }
 
-    // Node is not a root/domain node, and only contains 1 item.
-    if (depth > 1 && node.contents.length === 1) {
+    // Node is not a (1) thread and (2) root/domain node,
+    // and only contains 1 item.
+    if (depth > 2 && node.contents.length === 1) {
       const next = node.contents[0];
       // Do not collapse if the next node is a leaf node.
       if (next.type === "directory") {
diff --git a/devtools/client/debugger/src/utils/sources-tree/createTree.js b/devtools/client/debugger/src/utils/sources-tree/createTree.js
deleted file mode 100644
index 7eed7b6cdf1f..000000000000
--- a/devtools/client/debugger/src/utils/sources-tree/createTree.js
+++ /dev/null
@@ -1,36 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
-
-// @flow
-
-import { addToTree } from "./addToTree";
-import { collapseTree } from "./collapseTree";
-import { createDirectoryNode, createParentMap } from "./utils";
-import { getDomain } from "./treeOrder";
-
-import type { SourcesMap } from "../../reducers/types";
-import type { TreeDirectory } from "./types";
-
-type Params = {
-  sources: SourcesMap,
-  debuggeeUrl: string
-};
-
-export function createTree({ sources, debuggeeUrl }: Params) {
-  const uncollapsedTree = createDirectoryNode("root", "", []);
-  const debuggeeHost = getDomain(debuggeeUrl);
-
-  for (const sourceId in sources) {
-    const source = sources[sourceId];
-    addToTree(uncollapsedTree, source, debuggeeHost);
-  }
-
-  const sourceTree = collapseTree((uncollapsedTree: TreeDirectory));
-
-  return {
-    uncollapsedTree,
-    sourceTree,
-    parentMap: createParentMap(sourceTree)
-  };
-}
diff --git a/devtools/client/debugger/src/utils/sources-tree/index.js b/devtools/client/debugger/src/utils/sources-tree/index.js
index 335e2fd61f5a..102e73a70ace 100644
--- a/devtools/client/debugger/src/utils/sources-tree/index.js
+++ b/devtools/client/debugger/src/utils/sources-tree/index.js
@@ -11,11 +11,10 @@
 
 export { addToTree } from "./addToTree";
 export { collapseTree } from "./collapseTree";
-export { createTree } from "./createTree";
 export { formatTree } from "./formatTree";
 export { getDirectories } from "./getDirectories";
 export { getFilenameFromPath, getURL } from "./getURL";
-export { sortEntireTree, sortTree } from "./sortTree";
-export { updateTree } from "./updateTree";
+export { sortTree } from "./sortTree";
+export { createTree, updateTree } from "./updateTree";
 
 export * from "./utils";
diff --git a/devtools/client/debugger/src/utils/sources-tree/moz.build b/devtools/client/debugger/src/utils/sources-tree/moz.build
index 4550973c166b..0288b56d311a 100644
--- a/devtools/client/debugger/src/utils/sources-tree/moz.build
+++ b/devtools/client/debugger/src/utils/sources-tree/moz.build
@@ -10,7 +10,6 @@ DIRS += [
 CompiledModules(
     'addToTree.js',
     'collapseTree.js',
-    'createTree.js',
     'formatTree.js',
     'getDirectories.js',
     'getURL.js',
diff --git a/devtools/client/debugger/src/utils/sources-tree/sortTree.js b/devtools/client/debugger/src/utils/sources-tree/sortTree.js
index 77eff3aba324..5bf8f0e92201 100644
--- a/devtools/client/debugger/src/utils/sources-tree/sortTree.js
+++ b/devtools/client/debugger/src/utils/sources-tree/sortTree.js
@@ -8,25 +8,6 @@ import { nodeHasChildren, isExactUrlMatch } from "./utils";
 
 import type { TreeDirectory } from "./types";
 
-/**
- * Look at the nodes in the source tree, and determine the index of where to
- * insert a new node. The ordering is index -> folder -> file.
- * @memberof utils/sources-tree
- * @static
- */
-export function sortEntireTree(
-  tree: TreeDirectory,
-  debuggeeUrl: string = ""
-): TreeDirectory {
-  if (nodeHasChildren(tree)) {
-    const contents = sortTree(tree, debuggeeUrl).map((subtree: any) =>
-      sortEntireTree(subtree)
-    );
-    return { ...tree, contents };
-  }
-  return tree;
-}
-
 /**
  * Look at the nodes in the source tree, and determine the index of where to
  * insert a new node. The ordering is index -> folder -> file.
diff --git a/devtools/client/debugger/src/utils/sources-tree/tests/__snapshots__/addToTree.spec.js.snap b/devtools/client/debugger/src/utils/sources-tree/tests/__snapshots__/addToTree.spec.js.snap
index e31a7543420c..7059aced63f5 100644
--- a/devtools/client/debugger/src/utils/sources-tree/tests/__snapshots__/addToTree.spec.js.snap
+++ b/devtools/client/debugger/src/utils/sources-tree/tests/__snapshots__/addToTree.spec.js.snap
@@ -2,77 +2,90 @@
 
 exports[`sources-tree addToTree can add a file to an intermediate directory 1`] = `
 " - root path= 
-  - unpkg.com path=unpkg.com 
-    - codemirror@5.1 path=unpkg.com/codemirror@5.1 
-      - mode path=unpkg.com/codemirror@5.1/mode 
-        - xml path=unpkg.com/codemirror@5.1/mode/xml 
-          - xml.js path=unpkg.com/codemirror@5.1/mode/xml/xml.js source_id=server1.conn13.child1/39 
-    - codemirror@5.1 path=unpkg.com/codemirror@5.1 source_id=server1.conn13.child1/37 
+  - FakeThread path=FakeThread 
+    - unpkg.com path=FakeThread/unpkg.com 
+      - codemirror@5.1 path=FakeThread/unpkg.com/codemirror@5.1 
+        - mode path=FakeThread/unpkg.com/codemirror@5.1/mode 
+          - xml path=FakeThread/unpkg.com/codemirror@5.1/mode/xml 
+            - xml.js path=FakeThread/unpkg.com/codemirror@5.1/mode/xml/xml.js source_id=server1.conn13.child1/39 
+      - codemirror@5.1 path=FakeThread/unpkg.com/codemirror@5.1 source_id=server1.conn13.child1/37 
 "
 `;
 
 exports[`sources-tree addToTree correctly parses file sources 1`] = `
 " - root path= 
-  - file:// path=file:// 
-    - a path=file:///a 
-      - b.js path=file:///a/b.js source_id=actor1 
+  - FakeThread path=FakeThread 
+    - file:// path=FakeThread/file:// 
+      - a path=FakeThread/file:///a 
+        - b.js path=FakeThread/file:///a/b.js source_id=actor1 
 "
 `;
 
 exports[`sources-tree addToTree does not attempt to add two of the same directory 1`] = `
 " - root path= 
-  - davidwalsh.name path=davidwalsh.name 
-    - (index) path=https://davidwalsh.name/ source_id=server1.conn13.child1/37 
-    - wp-content path=davidwalsh.name/wp-content 
-      - prism.js path=davidwalsh.name/wp-content/prism.js source_id=server1.conn13.child1/39 
+  - FakeThread path=FakeThread 
+    - davidwalsh.name path=FakeThread/davidwalsh.name 
+      - (index) path=https://davidwalsh.name/ source_id=server1.conn13.child1/37 
+      - wp-content path=FakeThread/davidwalsh.name/wp-content 
+        - prism.js path=FakeThread/davidwalsh.name/wp-content/prism.js source_id=server1.conn13.child1/39 
 "
 `;
 
 exports[`sources-tree addToTree does not attempt to add two of the same file 1`] = `
 " - root path= 
-  - davidwalsh.name path=davidwalsh.name 
-    - (index) path=https://davidwalsh.name/ source_id=server1.conn13.child1/37 
+  - FakeThread path=FakeThread 
+    - davidwalsh.name path=FakeThread/davidwalsh.name 
+      - (index) path=https://davidwalsh.name/ source_id=server1.conn13.child1/39 
+      - util.js path=FakeThread/davidwalsh.name/util.js source_id=server1.conn13.child1/37 
+  - FakeThread2 path=FakeThread2 
+    - davidwalsh.name path=FakeThread2/davidwalsh.name 
+      - util.js path=FakeThread2/davidwalsh.name/util.js source_id=server1.conn13.child1/37 
 "
 `;
 
 exports[`sources-tree addToTree does not mangle encoded URLs 1`] = `
 " - root path= 
-  - example.com path=example.com 
-    - foo path=example.com/foo 
-      - B9724220.131821496;dc_ver=42.111;sz=468x60;u_sd=2;dc_adk=2020465299;ord=a53rpc;dc_rfl=1,https%3A%2F%2Fdavidwalsh.name%2F$0;xdt=1 path=example.com/foo/B9724220.131821496;dc_ver=42.111;sz=468x60;u_sd=2;dc_adk=2020465299;ord=a53rpc;dc_rfl=1,https%3A%2F%2Fdavidwalsh.name%2F$0;xdt=1 source_id=actor1 
+  - FakeThread path=FakeThread 
+    - example.com path=FakeThread/example.com 
+      - foo path=FakeThread/example.com/foo 
+        - B9724220.131821496;dc_ver=42.111;sz=468x60;u_sd=2;dc_adk=2020465299;ord=a53rpc;dc_rfl=1,https%3A%2F%2Fdavidwalsh.name%2F$0;xdt=1 path=FakeThread/example.com/foo/B9724220.131821496;dc_ver=42.111;sz=468x60;u_sd=2;dc_adk=2020465299;ord=a53rpc;dc_rfl=1,https%3A%2F%2Fdavidwalsh.name%2F$0;xdt=1 source_id=actor1 
 "
 `;
 
 exports[`sources-tree addToTree excludes javascript: URLs from the tree 1`] = `
 " - root path= 
-  - example.com path=example.com 
-    - source1.js path=example.com/source1.js source_id=actor2 
+  - FakeThread path=FakeThread 
+    - example.com path=FakeThread/example.com 
+      - source1.js path=FakeThread/example.com/source1.js source_id=actor2 
 "
 `;
 
 exports[`sources-tree addToTree name does not include query params 1`] = `
 " - root path= 
-  - example.com path=example.com 
-    - foo path=example.com/foo 
-      - name.js path=example.com/foo/name.js source_id=actor1 
+  - FakeThread path=FakeThread 
+    - example.com path=FakeThread/example.com 
+      - foo path=FakeThread/example.com/foo 
+        - name.js path=FakeThread/example.com/foo/name.js source_id=actor1 
 "
 `;
 
 exports[`sources-tree addToTree replaces a file with a directory 1`] = `
 " - root path= 
-  - unpkg.com path=unpkg.com 
-    - codemirror@5.1 path=unpkg.com/codemirror@5.1 
-      - mode path=unpkg.com/codemirror@5.1/mode 
-        - xml path=unpkg.com/codemirror@5.1/mode/xml 
-          - xml.js path=unpkg.com/codemirror@5.1/mode/xml/xml.js source_id=server1.conn13.child1/39 
-    - codemirror@5.1 path=unpkg.com/codemirror@5.1 source_id=server1.conn13.child1/37 
+  - FakeThread path=FakeThread 
+    - unpkg.com path=FakeThread/unpkg.com 
+      - codemirror@5.1 path=FakeThread/unpkg.com/codemirror@5.1 
+        - mode path=FakeThread/unpkg.com/codemirror@5.1/mode 
+          - xml path=FakeThread/unpkg.com/codemirror@5.1/mode/xml 
+            - xml.js path=FakeThread/unpkg.com/codemirror@5.1/mode/xml/xml.js source_id=server1.conn13.child1/39 
+      - codemirror@5.1 path=FakeThread/unpkg.com/codemirror@5.1 source_id=server1.conn13.child1/37 
 "
 `;
 
 exports[`sources-tree addToTree supports data URLs 1`] = `
 " - root path= 
-  - (no domain) path=(no domain) 
-    - data:text/html,<script>console.log(123)</script> path=data:text/html,<script>console.log(123)</script> source_id=server1.conn13.child1/39 
+  - FakeThread path=FakeThread 
+    - (no domain) path=FakeThread/(no domain) 
+      - data:text/html,<script>console.log(123)</script> path=data:text/html,<script>console.log(123)</script> source_id=server1.conn13.child1/39 
 "
 `;
 
diff --git a/devtools/client/debugger/src/utils/sources-tree/tests/__snapshots__/collapseTree.spec.js.snap b/devtools/client/debugger/src/utils/sources-tree/tests/__snapshots__/collapseTree.spec.js.snap
index bdad26c16fc0..529874f8bdc6 100644
--- a/devtools/client/debugger/src/utils/sources-tree/tests/__snapshots__/collapseTree.spec.js.snap
+++ b/devtools/client/debugger/src/utils/sources-tree/tests/__snapshots__/collapseTree.spec.js.snap
@@ -2,37 +2,41 @@
 
 exports[`sources tree collapseTree can collapse a single source 1`] = `
 " - root path= 
-  - example.com path=example.com 
-    - a/b path=example.com/a/b 
-      - c.js path=example.com/a/b/c.js source_id=actor1 
+  - Main Thread path=Main Thread 
+    - example.com path=Main Thread/example.com 
+      - a/b path=Main Thread/example.com/a/b 
+        - c.js path=Main Thread/example.com/a/b/c.js source_id=actor1 
 "
 `;
 
 exports[`sources tree collapseTree correctly merges in a collapsed source with a deeper level 1`] = `
 " - root path= 
-  - example.com path=example.com 
-    - a/b path=example.com/a/b 
-      - c/d path=example.com/a/b/c/d 
-        - e.js path=example.com/a/b/c/d/e.js source_id=actor2 
-      - c.js path=example.com/a/b/c.js source_id=actor1 
+  - Main Thread path=Main Thread 
+    - example.com path=Main Thread/example.com 
+      - a/b path=Main Thread/example.com/a/b 
+        - c/d path=Main Thread/example.com/a/b/c/d 
+          - e.js path=Main Thread/example.com/a/b/c/d/e.js source_id=actor2 
+        - c.js path=Main Thread/example.com/a/b/c.js source_id=actor1 
 "
 `;
 
 exports[`sources tree collapseTree correctly merges in a collapsed source with a shallower level 1`] = `
 " - root path= 
-  - example.com path=example.com 
-    - a/b path=example.com/a/b 
-      - c.js path=example.com/a/b/c.js source_id=actor1 
-      - x.js path=example.com/a/b/x.js source_id=actor3 
+  - Main Thread path=Main Thread 
+    - example.com path=Main Thread/example.com 
+      - a/b path=Main Thread/example.com/a/b 
+        - c.js path=Main Thread/example.com/a/b/c.js source_id=actor1 
+        - x.js path=Main Thread/example.com/a/b/x.js source_id=actor3 
 "
 `;
 
 exports[`sources tree collapseTree correctly merges in a collapsed source with the same level 1`] = `
 " - root path= 
-  - example.com path=example.com 
-    - a/b path=example.com/a/b 
-      - c/d path=example.com/a/b/c/d 
-        - e.js path=example.com/a/b/c/d/e.js source_id=actor2 
-      - c.js path=example.com/a/b/c.js source_id=actor1 
+  - Main Thread path=Main Thread 
+    - example.com path=Main Thread/example.com 
+      - a/b path=Main Thread/example.com/a/b 
+        - c/d path=Main Thread/example.com/a/b/c/d 
+          - e.js path=Main Thread/example.com/a/b/c/d/e.js source_id=actor2 
+        - c.js path=Main Thread/example.com/a/b/c.js source_id=actor1 
 "
 `;
diff --git a/devtools/client/debugger/src/utils/sources-tree/tests/__snapshots__/sortTree.spec.js.snap b/devtools/client/debugger/src/utils/sources-tree/tests/__snapshots__/sortTree.spec.js.snap
deleted file mode 100644
index e8120f8cb3d9..000000000000
--- a/devtools/client/debugger/src/utils/sources-tree/tests/__snapshots__/sortTree.spec.js.snap
+++ /dev/null
@@ -1,73 +0,0 @@
-// Jest Snapshot v1, https://goo.gl/fbAQLP
-
-exports[`sources-tree sortEntireTree alphabetically sorts children 1`] = `
-" - root path= 
-  - example.com path=example.com 
-    - foo path=example.com/foo 
-      - a_source3.js path=example.com/foo/a_source3.js source_id=actor3 
-      - b_source2.js path=example.com/foo/b_source2.js source_id=actor2 
-    - source1.js path=example.com/source1.js source_id=actor1 
-"
-`;
-
-exports[`sources-tree sortEntireTree puts folder at the top of the sort 1`] = `
-" - root path= 
-  - example.com path=example.com 
-    - folder path=example.com/folder 
-      - b path=example.com/folder/b 
-        - b.js path=example.com/folder/b/b.js source_id=actor2 
-      - c path=example.com/folder/c 
-        - (index) path=http://example.com/folder/c/ source_id=actor3 
-      - a.js path=example.com/folder/a.js source_id=actor1 
-"
-`;
-
-exports[`sources-tree sortEntireTree puts root debugee url at the top of the sort 1`] = `
-" - root path= 
-  - example.com path=example.com 
-    - b.js path=example.com/b.js source_id=actor2 
-  - api.example.com path=api.example.com 
-    - a.js path=api.example.com/a.js source_id=actor1 
-  - demo.com path=demo.com 
-    - c.js path=demo.com/c.js source_id=actor3 
-"
-`;
-
-exports[`sources-tree sortEntireTree puts root debugee url at the top of the sort 2`] = `
-" - root path= 
-  - demo.com path=demo.com 
-    - c.js path=demo.com/c.js source_id=actor3 
-  - api.example.com path=api.example.com 
-    - a.js path=api.example.com/a.js source_id=actor1 
-  - example.com path=example.com 
-    - b.js path=example.com/b.js source_id=actor2 
-"
-`;
-
-exports[`sources-tree sortEntireTree sorts folders first 1`] = `
-" - root path= 
-  - example.com path=example.com 
-    - (index) path=http://example.com source_id=actor4 
-    - b.js path=example.com/b.js 
-      - b_source.js path=example.com/b.js/b_source.js source_id=actor2 
-    - d path=example.com/d 
-      - d_source.js path=example.com/d/d_source.js source_id=actor5 
-    - a.js path=example.com/a.js source_id=actor1 
-    - b2 path=example.com/b2 source_id=actor6 
-    - c.js path=example.com/c.js source_id=actor3 
-"
-`;
-
-exports[`sources-tree sortEntireTree sorts folders first 2`] = `
-" - root path= 
-  - example.com path=example.com 
-    - (index) path=http://example.com source_id=actor4 
-    - b.js path=example.com/b.js 
-      - b_source.js path=example.com/b.js/b_source.js source_id=actor2 
-    - d path=example.com/d 
-      - d_source.js path=example.com/d/d_source.js source_id=actor5 
-    - a.js path=example.com/a.js source_id=actor1 
-    - b2 path=example.com/b2 source_id=actor6 
-    - c.js path=example.com/c.js source_id=actor3 
-"
-`;
diff --git a/devtools/client/debugger/src/utils/sources-tree/tests/__snapshots__/updateTree.spec.js.snap b/devtools/client/debugger/src/utils/sources-tree/tests/__snapshots__/updateTree.spec.js.snap
index f2c2e0ee07bc..1de925f0864a 100644
--- a/devtools/client/debugger/src/utils/sources-tree/tests/__snapshots__/updateTree.spec.js.snap
+++ b/devtools/client/debugger/src/utils/sources-tree/tests/__snapshots__/updateTree.spec.js.snap
@@ -8,38 +8,45 @@ exports[`calls updateTree.js adds one source 1`] = `
   \\"contents\\": [
     {
       \\"type\\": \\"directory\\",
-      \\"name\\": \\"davidwalsh.name\\",
-      \\"path\\": \\"davidwalsh.name\\",
+      \\"name\\": \\"FakeThread\\",
+      \\"path\\": \\"FakeThread\\",
       \\"contents\\": [
         {
-          \\"type\\": \\"source\\",
-          \\"name\\": \\"(index)\\",
-          \\"path\\": \\"https://davidwalsh.name/\\",
-          \\"contents\\": {
-            \\"id\\": \\"server1.conn13.child1/39\\",
-            \\"url\\": \\"https://davidwalsh.name/\\",
-            \\"isBlackBoxed\\": false,
-            \\"isPrettyPrinted\\": false,
-            \\"relativeUrl\\": \\"https://davidwalsh.name/\\",
-            \\"introductionUrl\\": null,
-            \\"isWasm\\": false,
-            \\"isExtension\\": false
-          }
-        },
-        {
-          \\"type\\": \\"source\\",
-          \\"name\\": \\"source1.js\\",
-          \\"path\\": \\"davidwalsh.name/source1.js\\",
-          \\"contents\\": {
-            \\"id\\": \\"server1.conn13.child1/37\\",
-            \\"url\\": \\"https://davidwalsh.name/source1.js\\",
-            \\"isBlackBoxed\\": false,
-            \\"isPrettyPrinted\\": false,
-            \\"relativeUrl\\": \\"https://davidwalsh.name/source1.js\\",
-            \\"introductionUrl\\": null,
-            \\"isWasm\\": false,
-            \\"isExtension\\": false
-          }
+          \\"type\\": \\"directory\\",
+          \\"name\\": \\"davidwalsh.name\\",
+          \\"path\\": \\"FakeThread/davidwalsh.name\\",
+          \\"contents\\": [
+            {
+              \\"type\\": \\"source\\",
+              \\"name\\": \\"(index)\\",
+              \\"path\\": \\"https://davidwalsh.name/\\",
+              \\"contents\\": {
+                \\"id\\": \\"server1.conn13.child1/39\\",
+                \\"url\\": \\"https://davidwalsh.name/\\",
+                \\"isBlackBoxed\\": false,
+                \\"isPrettyPrinted\\": false,
+                \\"relativeUrl\\": \\"https://davidwalsh.name/\\",
+                \\"introductionUrl\\": null,
+                \\"isWasm\\": false,
+                \\"isExtension\\": false
+              }
+            },
+            {
+              \\"type\\": \\"source\\",
+              \\"name\\": \\"source1.js\\",
+              \\"path\\": \\"FakeThread/davidwalsh.name/source1.js\\",
+              \\"contents\\": {
+                \\"id\\": \\"server1.conn13.child1/37\\",
+                \\"url\\": \\"https://davidwalsh.name/source1.js\\",
+                \\"isBlackBoxed\\": false,
+                \\"isPrettyPrinted\\": false,
+                \\"relativeUrl\\": \\"https://davidwalsh.name/source1.js\\",
+                \\"introductionUrl\\": null,
+                \\"isWasm\\": false,
+                \\"isExtension\\": false
+              }
+            }
+          ]
         }
       ]
     }
@@ -55,53 +62,60 @@ exports[`calls updateTree.js adds two sources 1`] = `
   \\"contents\\": [
     {
       \\"type\\": \\"directory\\",
-      \\"name\\": \\"davidwalsh.name\\",
-      \\"path\\": \\"davidwalsh.name\\",
+      \\"name\\": \\"FakeThread\\",
+      \\"path\\": \\"FakeThread\\",
       \\"contents\\": [
         {
-          \\"type\\": \\"source\\",
-          \\"name\\": \\"(index)\\",
-          \\"path\\": \\"https://davidwalsh.name/\\",
-          \\"contents\\": {
-            \\"id\\": \\"server1.conn13.child1/39\\",
-            \\"url\\": \\"https://davidwalsh.name/\\",
-            \\"isBlackBoxed\\": false,
-            \\"isPrettyPrinted\\": false,
-            \\"relativeUrl\\": \\"https://davidwalsh.name/\\",
-            \\"introductionUrl\\": null,
-            \\"isWasm\\": false,
-            \\"isExtension\\": false
-          }
-        },
-        {
-          \\"type\\": \\"source\\",
-          \\"name\\": \\"source1.js\\",
-          \\"path\\": \\"davidwalsh.name/source1.js\\",
-          \\"contents\\": {
-            \\"id\\": \\"server1.conn13.child1/37\\",
-            \\"url\\": \\"https://davidwalsh.name/source1.js\\",
-            \\"isBlackBoxed\\": false,
-            \\"isPrettyPrinted\\": false,
-            \\"relativeUrl\\": \\"https://davidwalsh.name/source1.js\\",
-            \\"introductionUrl\\": null,
-            \\"isWasm\\": false,
-            \\"isExtension\\": false
-          }
-        },
-        {
-          \\"type\\": \\"source\\",
-          \\"name\\": \\"source2.js\\",
-          \\"path\\": \\"davidwalsh.name/source2.js\\",
-          \\"contents\\": {
-            \\"id\\": \\"server1.conn13.child1/40\\",
-            \\"url\\": \\"https://davidwalsh.name/source2.js\\",
-            \\"isBlackBoxed\\": false,
-            \\"isPrettyPrinted\\": false,
-            \\"relativeUrl\\": \\"https://davidwalsh.name/source2.js\\",
-            \\"introductionUrl\\": null,
-            \\"isWasm\\": false,
-            \\"isExtension\\": false
-          }
+          \\"type\\": \\"directory\\",
+          \\"name\\": \\"davidwalsh.name\\",
+          \\"path\\": \\"FakeThread/davidwalsh.name\\",
+          \\"contents\\": [
+            {
+              \\"type\\": \\"source\\",
+              \\"name\\": \\"(index)\\",
+              \\"path\\": \\"https://davidwalsh.name/\\",
+              \\"contents\\": {
+                \\"id\\": \\"server1.conn13.child1/39\\",
+                \\"url\\": \\"https://davidwalsh.name/\\",
+                \\"isBlackBoxed\\": false,
+                \\"isPrettyPrinted\\": false,
+                \\"relativeUrl\\": \\"https://davidwalsh.name/\\",
+                \\"introductionUrl\\": null,
+                \\"isWasm\\": false,
+                \\"isExtension\\": false
+              }
+            },
+            {
+              \\"type\\": \\"source\\",
+              \\"name\\": \\"source1.js\\",
+              \\"path\\": \\"FakeThread/davidwalsh.name/source1.js\\",
+              \\"contents\\": {
+                \\"id\\": \\"server1.conn13.child1/37\\",
+                \\"url\\": \\"https://davidwalsh.name/source1.js\\",
+                \\"isBlackBoxed\\": false,
+                \\"isPrettyPrinted\\": false,
+                \\"relativeUrl\\": \\"https://davidwalsh.name/source1.js\\",
+                \\"introductionUrl\\": null,
+                \\"isWasm\\": false,
+                \\"isExtension\\": false
+              }
+            },
+            {
+              \\"type\\": \\"source\\",
+              \\"name\\": \\"source2.js\\",
+              \\"path\\": \\"FakeThread/davidwalsh.name/source2.js\\",
+              \\"contents\\": {
+                \\"id\\": \\"server1.conn13.child1/40\\",
+                \\"url\\": \\"https://davidwalsh.name/source2.js\\",
+                \\"isBlackBoxed\\": false,
+                \\"isPrettyPrinted\\": false,
+                \\"relativeUrl\\": \\"https://davidwalsh.name/source2.js\\",
+                \\"introductionUrl\\": null,
+                \\"isWasm\\": false,
+                \\"isExtension\\": false
+              }
+            }
+          ]
         }
       ]
     }
@@ -117,38 +131,30 @@ exports[`calls updateTree.js shows all the sources 1`] = `
   \\"contents\\": [
     {
       \\"type\\": \\"directory\\",
-      \\"name\\": \\"davidwalsh.name\\",
-      \\"path\\": \\"davidwalsh.name\\",
+      \\"name\\": \\"FakeThread\\",
+      \\"path\\": \\"FakeThread\\",
       \\"contents\\": [
         {
-          \\"type\\": \\"source\\",
-          \\"name\\": \\"(index)\\",
-          \\"path\\": \\"https://davidwalsh.name/\\",
-          \\"contents\\": {
-            \\"id\\": \\"server1.conn13.child1/39\\",
-            \\"url\\": \\"https://davidwalsh.name/\\",
-            \\"isBlackBoxed\\": false,
-            \\"isPrettyPrinted\\": false,
-            \\"relativeUrl\\": \\"https://davidwalsh.name/\\",
-            \\"introductionUrl\\": null,
-            \\"isWasm\\": false,
-            \\"isExtension\\": false
-          }
-        },
-        {
-          \\"type\\": \\"source\\",
-          \\"name\\": \\"source1.js\\",
-          \\"path\\": \\"davidwalsh.name/source1.js\\",
-          \\"contents\\": {
-            \\"id\\": \\"server1.conn13.child1/37\\",
-            \\"url\\": \\"https://davidwalsh.name/source1.js\\",
-            \\"isBlackBoxed\\": false,
-            \\"isPrettyPrinted\\": false,
-            \\"relativeUrl\\": \\"https://davidwalsh.name/source1.js\\",
-            \\"introductionUrl\\": null,
-            \\"isWasm\\": false,
-            \\"isExtension\\": false
-          }
+          \\"type\\": \\"directory\\",
+          \\"name\\": \\"davidwalsh.name\\",
+          \\"path\\": \\"FakeThread/davidwalsh.name\\",
+          \\"contents\\": [
+            {
+              \\"type\\": \\"source\\",
+              \\"name\\": \\"(index)\\",
+              \\"path\\": \\"https://davidwalsh.name/\\",
+              \\"contents\\": {
+                \\"id\\": \\"server1.conn13.child1/39\\",
+                \\"url\\": \\"https://davidwalsh.name/\\",
+                \\"isBlackBoxed\\": false,
+                \\"isPrettyPrinted\\": false,
+                \\"relativeUrl\\": \\"https://davidwalsh.name/\\",
+                \\"introductionUrl\\": null,
+                \\"isWasm\\": false,
+                \\"isExtension\\": false
+              }
+            }
+          ]
         }
       ]
     }
diff --git a/devtools/client/debugger/src/utils/sources-tree/tests/addToTree.spec.js b/devtools/client/debugger/src/utils/sources-tree/tests/addToTree.spec.js
index 37daf84da674..ea5cccb41f90 100644
--- a/devtools/client/debugger/src/utils/sources-tree/tests/addToTree.spec.js
+++ b/devtools/client/debugger/src/utils/sources-tree/tests/addToTree.spec.js
@@ -17,7 +17,7 @@ import {
   nodeHasChildren
 } from "../index";
 
-type RawSource = {| url: string, id: string |};
+type RawSource = {| url: string, id: string, actors?: any |};
 
 function createSourcesMap(sources: RawSource[]) {
   const sourcesMap = sources.reduce((map, source) => {
@@ -63,10 +63,10 @@ describe("sources-tree", () => {
       );
       const tree = createDirectoryNode("root", "", []);
 
-      addToTree(tree, source1, "http://example.com/");
+      addToTree(tree, source1, "http://example.com/", "FakeThread");
       expect(tree.contents).toHaveLength(1);
 
-      const base = tree.contents[0];
+      const base = tree.contents[0].contents[0];
       expect(base.name).toBe("example.com");
       expect(base.contents).toHaveLength(1);
 
@@ -89,8 +89,8 @@ describe("sources-tree", () => {
 
       const tree = createDirectoryNode("root", "", []);
 
-      addToTree(tree, source1, "http://example.com/");
-      const childNode = getChildNode(tree, 0, 0, 0);
+      addToTree(tree, source1, "http://example.com/", "FakeThread");
+      const childNode = getChildNode(tree, 0, 0, 0, 0);
       expect(childNode.name).toEqual(sourceName);
       expect(formatTree(tree)).toMatchSnapshot();
     });
@@ -105,7 +105,7 @@ describe("sources-tree", () => {
 
       const tree = createDirectoryNode("root", "", []);
 
-      addToTree(tree, source1, "http://example.com/");
+      addToTree(tree, source1, "http://example.com/", "FakeThread");
       expect(formatTree(tree)).toMatchSnapshot();
     });
 
@@ -121,14 +121,22 @@ describe("sources-tree", () => {
         }
       ];
 
-      const sourceMap = createSourcesMap(sources);
+      const sourceMap = { FakeThread: createSourcesMap(sources) };
       const tree = createTree({
         sources: sourceMap,
         debuggeeUrl: "",
-        projectRoot: ""
+        threads: [
+          {
+            actor: "FakeThread",
+            name: "FakeThread",
+            url: "https://davidwalsh.name",
+            type: 1
+          }
+        ]
       }).sourceTree;
-      // expect(tree.contents).toHaveLength(1);
-      const subtree = tree.contents[0];
+
+      expect(tree.contents[0].contents).toHaveLength(1);
+      const subtree = tree.contents[0].contents[0];
       expect(subtree.contents).toHaveLength(2);
       expect(formatTree(tree)).toMatchSnapshot();
     });
@@ -141,11 +149,18 @@ describe("sources-tree", () => {
         }
       ];
 
-      const sourceMap = createSourcesMap(sources);
+      const sourceMap = { FakeThread: createSourcesMap(sources) };
       const tree = createTree({
         sources: sourceMap,
         debuggeeUrl: "",
-        projectRoot: ""
+        threads: [
+          {
+            actor: "FakeThread",
+            url: "https://davidwalsh.name",
+            type: 1,
+            name: "FakeThread"
+          }
+        ]
       }).sourceTree;
       expect(formatTree(tree)).toMatchSnapshot();
     });
@@ -158,19 +173,39 @@ describe("sources-tree", () => {
         },
         {
           id: "server1.conn13.child1/37",
-          url: "https://davidwalsh.name/"
+          url: "https://davidwalsh.name/util.js"
         }
       ];
 
-      const sourceMap = createSourcesMap(sources);
+      const sourceMap = {
+        FakeThread: createSourcesMap(sources),
+        FakeThread2: createSourcesMap([sources[1]])
+      };
+
       const tree = createTree({
         sources: sourceMap,
-        debuggeeUrl: "",
-        projectRoot: ""
+        debuggeeUrl: "https://davidwalsh.name",
+        threads: [
+          {
+            actor: "FakeThread",
+            name: "FakeThread",
+            url: "https://davidwalsh.name",
+            type: 1
+          },
+          {
+            actor: "FakeThread2",
+            name: "FakeThread2",
+            url: "https://davidwalsh.name/WorkerA.js",
+            type: 2
+          }
+        ]
       }).sourceTree;
-      expect(tree.contents).toHaveLength(1);
-      const subtree = tree.contents[0];
-      expect(subtree.contents).toHaveLength(1);
+
+      expect(tree.contents[0].contents).toHaveLength(1);
+      const subtree = tree.contents[0].contents[0];
+      expect(subtree.contents).toHaveLength(2);
+      const subtree2 = tree.contents[1].contents[0];
+      expect(subtree2.contents).toHaveLength(1);
       expect(formatTree(tree)).toMatchSnapshot();
     });
 
@@ -186,11 +221,11 @@ describe("sources-tree", () => {
       );
       const tree = createDirectoryNode("root", "", []);
 
-      addToTree(tree, source1, "http://example.com/");
-      addToTree(tree, source2, "http://example.com/");
-      addToTree(tree, source3, "http://example.com/");
+      addToTree(tree, source1, "http://example.com/", "FakeThread");
+      addToTree(tree, source2, "http://example.com/", "FakeThread");
+      addToTree(tree, source3, "http://example.com/", "FakeThread");
 
-      const base = tree.contents[0];
+      const base = tree.contents[0].contents[0];
       expect(tree.contents).toHaveLength(1);
 
       const source1Node = base.contents[0];
@@ -202,10 +237,10 @@ describe("sources-tree", () => {
       const source = makeMockSource("file:///a/b.js", "actor1");
       const tree = createDirectoryNode("root", "", []);
 
-      addToTree(tree, source, "file:///a/index.html");
+      addToTree(tree, source, "file:///a/index.html", "FakeThread");
       expect(tree.contents).toHaveLength(1);
 
-      const base = tree.contents[0];
+      const base = tree.contents[0].contents[0];
       expect(base.name).toBe("file://");
       expect(base.contents).toHaveLength(1);
 
@@ -232,7 +267,9 @@ describe("sources-tree", () => {
 
       const sources = createSourcesList(testData);
       const tree = createDirectoryNode("root", "", []);
-      sources.forEach(source => addToTree(tree, source, "https://unpkg.com/"));
+      sources.forEach(source =>
+        addToTree(tree, source, "https://unpkg.com/", "FakeThread")
+      );
       expect(formatTree(tree)).toMatchSnapshot();
     });
 
@@ -251,7 +288,9 @@ describe("sources-tree", () => {
 
       const sources = createSourcesList(testData);
       const tree = createDirectoryNode("root", "", []);
-      sources.forEach(source => addToTree(tree, source, "https://unpkg.com/"));
+      sources.forEach(source =>
+        addToTree(tree, source, "https://unpkg.com/", "FakeThread")
+      );
       expect(formatTree(tree)).toMatchSnapshot();
     });
 
@@ -284,7 +323,7 @@ describe("sources-tree", () => {
       const domain = "http://localhost:4242";
       const sources = createSourcesList(testData);
       const tree = createDirectoryNode("root", "", []);
-      sources.forEach(source => addToTree(tree, source, domain));
+      sources.forEach(source => addToTree(tree, source, domain, "FakeThread"));
       expect(formatTree(tree)).toMatchSnapshot();
     });
   });
diff --git a/devtools/client/debugger/src/utils/sources-tree/tests/collapseTree.spec.js b/devtools/client/debugger/src/utils/sources-tree/tests/collapseTree.spec.js
index 5a9dbcf3e285..ad7dce2985a3 100644
--- a/devtools/client/debugger/src/utils/sources-tree/tests/collapseTree.spec.js
+++ b/devtools/client/debugger/src/utils/sources-tree/tests/collapseTree.spec.js
@@ -8,7 +8,6 @@ import { makeMockSource } from "../../../utils/test-mockup";
 
 import {
   collapseTree,
-  sortEntireTree,
   formatTree,
   addToTree,
   createDirectoryNode
@@ -22,11 +21,11 @@ describe("sources tree", () => {
   describe("collapseTree", () => {
     it("can collapse a single source", () => {
       const fullTree = createDirectoryNode("root", "", []);
-      addToTree(fullTree, abcSource, "http://example.com/");
+      addToTree(fullTree, abcSource, "http://example.com/", "Main Thread");
       expect(fullTree.contents).toHaveLength(1);
       const tree = collapseTree(fullTree);
 
-      const host = tree.contents[0];
+      const host = tree.contents[0].contents[0];
       expect(host.name).toBe("example.com");
       expect(host.contents).toHaveLength(1);
 
@@ -36,20 +35,17 @@ describe("sources tree", () => {
 
       const abcNode = abFolder.contents[0];
       expect(abcNode.name).toBe("c.js");
-      expect(abcNode.path).toBe("example.com/a/b/c.js");
+      expect(abcNode.path).toBe("Main Thread/example.com/a/b/c.js");
       expect(formatTree(tree)).toMatchSnapshot();
     });
 
     it("correctly merges in a collapsed source with a deeper level", () => {
       const fullTree = createDirectoryNode("root", "", []);
-      addToTree(fullTree, abcSource, "http://example.com/");
-      addToTree(fullTree, abcdeSource, "http://example.com/");
+      addToTree(fullTree, abcSource, "http://example.com/", "Main Thread");
+      addToTree(fullTree, abcdeSource, "http://example.com/", "Main Thread");
       const tree = collapseTree(fullTree);
 
-      sortEntireTree(tree);
-      expect(tree.contents).toHaveLength(1);
-
-      const host = tree.contents[0];
+      const host = tree.contents[0].contents[0];
       expect(host.name).toBe("example.com");
       expect(host.contents).toHaveLength(1);
 
@@ -59,24 +55,24 @@ describe("sources tree", () => {
 
       const [cdFolder, abcNode] = abFolder.contents;
       expect(abcNode.name).toBe("c.js");
-      expect(abcNode.path).toBe("example.com/a/b/c.js");
+      expect(abcNode.path).toBe("Main Thread/example.com/a/b/c.js");
       expect(cdFolder.name).toBe("c/d");
 
       const [abcdeNode] = cdFolder.contents;
       expect(abcdeNode.name).toBe("e.js");
-      expect(abcdeNode.path).toBe("example.com/a/b/c/d/e.js");
+      expect(abcdeNode.path).toBe("Main Thread/example.com/a/b/c/d/e.js");
       expect(formatTree(tree)).toMatchSnapshot();
     });
 
     it("correctly merges in a collapsed source with a shallower level", () => {
       const fullTree = createDirectoryNode("root", "", []);
-      addToTree(fullTree, abcSource, "http://example.com/");
-      addToTree(fullTree, abxSource, "http://example.com/");
+      addToTree(fullTree, abcSource, "http://example.com/", "Main Thread");
+      addToTree(fullTree, abxSource, "http://example.com/", "Main Thread");
       const tree = collapseTree(fullTree);
 
       expect(tree.contents).toHaveLength(1);
 
-      const host = tree.contents[0];
+      const host = tree.contents[0].contents[0];
       expect(host.name).toBe("example.com");
       expect(host.contents).toHaveLength(1);
 
@@ -86,21 +82,21 @@ describe("sources tree", () => {
 
       const [abcNode, abxNode] = abFolder.contents;
       expect(abcNode.name).toBe("c.js");
-      expect(abcNode.path).toBe("example.com/a/b/c.js");
+      expect(abcNode.path).toBe("Main Thread/example.com/a/b/c.js");
       expect(abxNode.name).toBe("x.js");
-      expect(abxNode.path).toBe("example.com/a/b/x.js");
+      expect(abxNode.path).toBe("Main Thread/example.com/a/b/x.js");
       expect(formatTree(tree)).toMatchSnapshot();
     });
 
     it("correctly merges in a collapsed source with the same level", () => {
       const fullTree = createDirectoryNode("root", "", []);
-      addToTree(fullTree, abcdeSource, "http://example.com/");
-      addToTree(fullTree, abcSource, "http://example.com/");
+      addToTree(fullTree, abcdeSource, "http://example.com/", "Main Thread");
+      addToTree(fullTree, abcSource, "http://example.com/", "Main Thread");
       const tree = collapseTree(fullTree);
 
       expect(tree.contents).toHaveLength(1);
 
-      const host = tree.contents[0];
+      const host = tree.contents[0].contents[0];
       expect(host.name).toBe("example.com");
       expect(host.contents).toHaveLength(1);
 
@@ -110,12 +106,12 @@ describe("sources tree", () => {
 
       const [cdFolder, abcNode] = abFolder.contents;
       expect(abcNode.name).toBe("c.js");
-      expect(abcNode.path).toBe("example.com/a/b/c.js");
+      expect(abcNode.path).toBe("Main Thread/example.com/a/b/c.js");
       expect(cdFolder.name).toBe("c/d");
 
       const [abcdeNode] = cdFolder.contents;
       expect(abcdeNode.name).toBe("e.js");
-      expect(abcdeNode.path).toBe("example.com/a/b/c/d/e.js");
+      expect(abcdeNode.path).toBe("Main Thread/example.com/a/b/c/d/e.js");
       expect(formatTree(tree)).toMatchSnapshot();
     });
   });
diff --git a/devtools/client/debugger/src/utils/sources-tree/tests/getDirectories.spec.js b/devtools/client/debugger/src/utils/sources-tree/tests/getDirectories.spec.js
index ccc499eae2ee..c3c472fe42d1 100644
--- a/devtools/client/debugger/src/utils/sources-tree/tests/getDirectories.spec.js
+++ b/devtools/client/debugger/src/utils/sources-tree/tests/getDirectories.spec.js
@@ -14,11 +14,13 @@ function formatDirectories(source, tree) {
 }
 
 function createSources(urls) {
-  return urls.reduce((sources, url, index) => {
-    const id = `a${index}`;
-    sources[id] = makeMockSource(url, id);
-    return sources;
-  }, {});
+  return {
+    FakeThread: urls.reduce((sources, url, index) => {
+      const id = `a${index}`;
+      sources[id] = makeMockSource(url, id);
+      return sources;
+    }, {})
+  };
 }
 
 describe("getDirectories", () => {
@@ -29,14 +31,36 @@ describe("getDirectories", () => {
       "http://b/c.js"
     ]);
 
+    const threads = [
+      {
+        actor: "FakeThread",
+        url: "http://a",
+        type: 1,
+        name: "FakeThread"
+      }
+    ];
+
     const debuggeeUrl = "http://a/";
     const { sourceTree } = createTree({
       sources,
       debuggeeUrl,
-      projectRoot: ""
+      threads
     });
-    expect(formatDirectories(sources.a0, sourceTree)).toEqual(["a/b.js", "a"]);
-    expect(formatDirectories(sources.a1, sourceTree)).toEqual(["a/c.js", "a"]);
-    expect(formatDirectories(sources.a2, sourceTree)).toEqual(["b/c.js", "b"]);
+
+    expect(formatDirectories(sources.FakeThread.a0, sourceTree)).toEqual([
+      "FakeThread/a/b.js",
+      "FakeThread/a",
+      "FakeThread"
+    ]);
+    expect(formatDirectories(sources.FakeThread.a1, sourceTree)).toEqual([
+      "FakeThread/a/c.js",
+      "FakeThread/a",
+      "FakeThread"
+    ]);
+    expect(formatDirectories(sources.FakeThread.a2, sourceTree)).toEqual([
+      "FakeThread/b/c.js",
+      "FakeThread/b",
+      "FakeThread"
+    ]);
   });
 });
diff --git a/devtools/client/debugger/src/utils/sources-tree/tests/sortTree.spec.js b/devtools/client/debugger/src/utils/sources-tree/tests/sortTree.spec.js
deleted file mode 100644
index 99cf1c5970e6..000000000000
--- a/devtools/client/debugger/src/utils/sources-tree/tests/sortTree.spec.js
+++ /dev/null
@@ -1,153 +0,0 @@
-/* eslint max-nested-callbacks: ["error", 4]*/
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
-
-// @flow
-
-import { makeMockSource } from "../../../utils/test-mockup";
-
-import {
-  addToTree,
-  sortEntireTree,
-  createDirectoryNode,
-  formatTree
-} from "../index";
-
-describe("sources-tree", () => {
-  describe("sortEntireTree", () => {
-    it("alphabetically sorts children", () => {
-      const source1 = makeMockSource("http://example.com/source1.js", "actor1");
-      const source2 = makeMockSource(
-        "http://example.com/foo/b_source2.js",
-        "actor2"
-      );
-      const source3 = makeMockSource(
-        "http://example.com/foo/a_source3.js",
-        "actor3"
-      );
-      const _tree = createDirectoryNode("root", "", []);
-
-      addToTree(_tree, source1, "http://example.com/");
-      addToTree(_tree, source2, "http://example.com/");
-      addToTree(_tree, source3, "http://example.com/");
-      const tree = sortEntireTree(_tree);
-
-      const base = tree.contents[0];
-      const fooNode = base.contents[0];
-      expect(fooNode.name).toBe("foo");
-      expect(fooNode.contents).toHaveLength(2);
-
-      const source1Node = base.contents[1];
-      expect(source1Node.name).toBe("source1.js");
-
-      // source2 should be after source1 alphabetically
-      const source2Node = fooNode.contents[1];
-      const source3Node = fooNode.contents[0];
-      expect(source2Node.name).toBe("b_source2.js");
-      expect(source3Node.name).toBe("a_source3.js");
-      expect(formatTree(tree)).toMatchSnapshot();
-    });
-
-    it("sorts folders first", () => {
-      const sources = [
-        makeMockSource("http://example.com/a.js", "actor1"),
-        makeMockSource("http://example.com/b.js/b_source.js", "actor2"),
-        makeMockSource("http://example.com/c.js", "actor3"),
-        makeMockSource("http://example.com", "actor4"),
-        makeMockSource("http://example.com/d/d_source.js", "actor5"),
-        makeMockSource("http://example.com/b2", "actor6")
-      ];
-
-      const _tree = createDirectoryNode("root", "", []);
-      sources.forEach(source =>
-        addToTree(_tree, source, "http://example.com/")
-      );
-      const tree = sortEntireTree(_tree);
-      const domain = tree.contents[0];
-
-      const [
-        indexNode,
-        bFolderNode,
-        dFolderNode,
-        aFileNode,
-        b2FileNode,
-        cFileNode
-      ] = domain.contents;
-
-      expect(formatTree(tree)).toMatchSnapshot();
-      expect(indexNode.name).toBe("(index)");
-      expect(bFolderNode.name).toBe("b.js");
-      expect(bFolderNode.contents).toHaveLength(1);
-      expect(bFolderNode.contents[0].name).toBe("b_source.js");
-
-      expect(b2FileNode.name).toBe("b2");
-
-      expect(dFolderNode.name).toBe("d");
-      expect(dFolderNode.contents).toHaveLength(1);
-      expect(dFolderNode.contents[0].name).toBe("d_source.js");
-
-      expect(aFileNode.name).toBe("a.js");
-
-      expect(cFileNode.name).toBe("c.js");
-      expect(formatTree(tree)).toMatchSnapshot();
-    });
-
-    it("puts folder at the top of the sort", () => {
-      const sources = [
-        makeMockSource("http://example.com/folder/a.js", "actor1"),
-        makeMockSource("http://example.com/folder/b/b.js", "actor2"),
-        makeMockSource("http://example.com/folder/c/", "actor3")
-      ];
-
-      const _tree = createDirectoryNode("root", "", []);
-      sources.forEach(source =>
-        addToTree(_tree, source, "http://example.com/")
-      );
-      const tree = sortEntireTree(_tree);
-      const [
-        bFolderNode,
-        cFolderNode,
-        aFileNode
-      ] = tree.contents[0].contents[0].contents;
-
-      expect(bFolderNode.name).toBe("b");
-      expect(bFolderNode.contents).toHaveLength(1);
-      expect(bFolderNode.contents[0].name).toBe("b.js");
-
-      expect(cFolderNode.name).toBe("c");
-      expect(cFolderNode.contents).toHaveLength(1);
-      expect(cFolderNode.contents[0].name).toBe("(index)");
-
-      expect(aFileNode.name).toBe("a.js");
-      expect(formatTree(tree)).toMatchSnapshot();
-    });
-
-    it("puts root debugee url at the top of the sort", () => {
-      const sources = [
-        makeMockSource("http://api.example.com/a.js", "actor1"),
-        makeMockSource("http://example.com/b.js", "actor2"),
-        makeMockSource("http://demo.com/c.js", "actor3")
-      ];
-
-      const rootA = "http://example.com/path/to/file.html";
-      const rootB = "https://www.demo.com/index.html";
-      const _treeA = createDirectoryNode("root", "", []);
-      const _treeB = createDirectoryNode("root", "", []);
-      sources.forEach(source => {
-        addToTree(_treeA, source, rootA);
-        addToTree(_treeB, source, rootB);
-      });
-      const treeA = sortEntireTree(_treeA, rootA);
-      const treeB = sortEntireTree(_treeB, rootB);
-
-      expect(treeA.contents[0].contents[0].name).toBe("b.js");
-      expect(treeA.contents[1].contents[0].name).toBe("a.js");
-
-      expect(treeB.contents[0].contents[0].name).toBe("c.js");
-      expect(treeB.contents[1].contents[0].name).toBe("a.js");
-      expect(formatTree(treeA)).toMatchSnapshot();
-      expect(formatTree(treeB)).toMatchSnapshot();
-    });
-  });
-});
diff --git a/devtools/client/debugger/src/utils/sources-tree/tests/updateTree.spec.js b/devtools/client/debugger/src/utils/sources-tree/tests/updateTree.spec.js
index bd09adcac8f5..386b177fc866 100644
--- a/devtools/client/debugger/src/utils/sources-tree/tests/updateTree.spec.js
+++ b/devtools/client/debugger/src/utils/sources-tree/tests/updateTree.spec.js
@@ -7,7 +7,7 @@
 import { makeMockSource } from "../../../utils/test-mockup";
 import { updateTree, createTree } from "../index";
 
-type RawSource = {| url: string, id: string |};
+type RawSource = {| url: string, id: string, actors?: any |};
 
 function createSourcesMap(sources: RawSource[]) {
   const sourcesMap = sources.reduce((map, source) => {
@@ -15,7 +15,7 @@ function createSourcesMap(sources: RawSource[]) {
     return map;
   }, {});
 
-  return sourcesMap;
+  return { FakeThread: sourcesMap };
 }
 
 function formatTree(tree) {
@@ -37,25 +37,32 @@ const sources = [
   }
 ];
 
+const threads = [
+  {
+    actor: "FakeThread",
+    url: "https://davidwalsh.name",
+    type: 1,
+    name: "FakeThread"
+  }
+];
+
 const debuggeeUrl = "blah";
 
 describe("calls updateTree.js", () => {
   it("adds one source", () => {
     const prevSources = createSourcesMap([sources[0]]);
-
     const { sourceTree, uncollapsedTree } = createTree({
       debuggeeUrl,
       sources: prevSources,
-      projectRoot: ""
+      threads
     });
-
     const newTree = updateTree({
       debuggeeUrl,
       prevSources,
       newSources: createSourcesMap([sources[0], sources[1]]),
       uncollapsedTree,
       sourceTree,
-      projectRoot: ""
+      threads
     });
 
     expect(formatTree(newTree)).toMatchSnapshot();
@@ -67,7 +74,7 @@ describe("calls updateTree.js", () => {
     const { sourceTree, uncollapsedTree } = createTree({
       debuggeeUrl,
       sources: prevSources,
-      projectRoot: ""
+      threads
     });
 
     const newTree = updateTree({
@@ -76,7 +83,8 @@ describe("calls updateTree.js", () => {
       newSources: createSourcesMap([sources[0], sources[1], sources[2]]),
       uncollapsedTree,
       sourceTree,
-      projectRoot: ""
+      projectRoot: "",
+      threads
     });
 
     expect(formatTree(newTree)).toMatchSnapshot();
@@ -90,7 +98,7 @@ describe("calls updateTree.js", () => {
     const { sourceTree, uncollapsedTree } = createTree({
       debuggeeUrl,
       sources: prevSources,
-      projectRoot: ""
+      threads
     });
 
     const newTree = updateTree({
@@ -99,7 +107,8 @@ describe("calls updateTree.js", () => {
       newSources: createSourcesMap([sources[1]]),
       uncollapsedTree,
       sourceTree,
-      projectRoot: ""
+      projectRoot: "",
+      threads
     });
 
     expect(formatTree(newTree)).toMatchSnapshot();
diff --git a/devtools/client/debugger/src/utils/sources-tree/tests/utils.spec.js b/devtools/client/debugger/src/utils/sources-tree/tests/utils.spec.js
index 4169d922a6c1..a6e6129e781d 100644
--- a/devtools/client/debugger/src/utils/sources-tree/tests/utils.spec.js
+++ b/devtools/client/debugger/src/utils/sources-tree/tests/utils.spec.js
@@ -13,7 +13,6 @@ import {
   isExactUrlMatch,
   isDirectory,
   addToTree,
-  sortEntireTree,
   isNotJavaScript
 } from "../index";
 
@@ -47,9 +46,10 @@ describe("sources tree", () => {
       ];
 
       const tree = createDirectoryNode("root", "", []);
-      sources.forEach(source => addToTree(tree, source, "http://example.com/"));
-      sortEntireTree(tree);
-      const [bFolderNode, aFileNode] = tree.contents[0].contents;
+      sources.forEach(source =>
+        addToTree(tree, source, "http://example.com/", "Main Thread")
+      );
+      const [bFolderNode, aFileNode] = tree.contents[0].contents[0].contents;
       const [cFolderNode] = bFolderNode.contents;
       const [dFileNode] = cFolderNode.contents;
 
diff --git a/devtools/client/debugger/src/utils/sources-tree/updateTree.js b/devtools/client/debugger/src/utils/sources-tree/updateTree.js
index c211ad038fa2..1085abdccd08 100644
--- a/devtools/client/debugger/src/utils/sources-tree/updateTree.js
+++ b/devtools/client/debugger/src/utils/sources-tree/updateTree.js
@@ -6,42 +6,82 @@
 
 import { addToTree } from "./addToTree";
 import { collapseTree } from "./collapseTree";
-import { createParentMap } from "./utils";
-import { difference } from "lodash";
+import { createDirectoryNode, createParentMap } from "./utils";
 import { getDomain } from "./treeOrder";
-import type { SourcesMap } from "../../reducers/types";
+
+import type { SourcesMapByThread } from "../../reducers/types";
+import type { Thread, Source } from "../../types";
 import type { TreeDirectory } from "./types";
 
-function newSourcesSet(newSources, prevSources) {
-  const newSourceIds = difference(
-    Object.keys(newSources),
-    Object.keys(prevSources)
-  );
-  const uniqSources = newSourceIds.map(id => newSources[id]);
-  return uniqSources;
+function getSourcesToAdd(newSources, prevSources): Source[] {
+  const sourcesToAdd = [];
+
+  for (const sourceId in newSources) {
+    const newSource = newSources[sourceId];
+    const prevSource = prevSources ? prevSources[sourceId] : null;
+    if (!prevSource) {
+      sourcesToAdd.push(newSource);
+    }
+  }
+
+  return sourcesToAdd;
 }
 
-type Params = {
-  newSources: SourcesMap,
-  prevSources: SourcesMap,
+type UpdateTreeParams = {
+  newSources: SourcesMapByThread,
+  prevSources: SourcesMapByThread,
   uncollapsedTree: TreeDirectory,
-  sourceTree: TreeDirectory,
-  debuggeeUrl: string
+  debuggeeUrl: string,
+  threads: Thread[]
 };
 
+type CreateTreeParams = {
+  sources: SourcesMapByThread,
+  debuggeeUrl: string,
+  threads: Thread[]
+};
+
+export function createTree({
+  debuggeeUrl,
+  sources,
+  threads
+}: CreateTreeParams) {
+  const uncollapsedTree = createDirectoryNode("root", "", []);
+
+  return updateTree({
+    debuggeeUrl,
+    newSources: sources,
+    prevSources: {},
+    threads,
+    uncollapsedTree
+  });
+}
+
 export function updateTree({
   newSources,
   prevSources,
   debuggeeUrl,
   uncollapsedTree,
-  sourceTree
-}: Params) {
-  const newSet = newSourcesSet(newSources, prevSources);
+  threads
+}: UpdateTreeParams) {
   const debuggeeHost = getDomain(debuggeeUrl);
+  const contexts = (Object.keys(newSources): any);
 
-  for (const source of newSet) {
-    addToTree(uncollapsedTree, source, debuggeeHost);
-  }
+  contexts.forEach(context => {
+    const thread = threads.find(t => t.actor === context);
+    if (!thread) {
+      return;
+    }
+
+    const sourcesToAdd = getSourcesToAdd(
+      (Object.values(newSources[context]): any),
+      prevSources[context] ? (Object.values(prevSources[context]): any) : null
+    );
+
+    for (const source of sourcesToAdd) {
+      addToTree(uncollapsedTree, source, debuggeeHost, thread.actor);
+    }
+  });
 
   const newSourceTree = collapseTree(uncollapsedTree);
 
diff --git a/devtools/client/debugger/src/utils/sources-tree/utils.js b/devtools/client/debugger/src/utils/sources-tree/utils.js
index d032a1bd8c89..4cf3dbe47e23 100644
--- a/devtools/client/debugger/src/utils/sources-tree/utils.js
+++ b/devtools/client/debugger/src/utils/sources-tree/utils.js
@@ -13,7 +13,7 @@ import { getURL } from "./getURL";
 const IGNORED_URLS = ["debugger eval code", "XStringBundle"];
 
 export function nodeHasChildren(item: TreeNode): boolean {
-  return Array.isArray(item.contents) && item.type === "directory";
+  return Array.isArray(item.contents) && item.type == "directory";
 }
 
 export function isExactUrlMatch(pathPart: string, debuggeeUrl: string) {
diff --git a/devtools/client/debugger/test/mochitest/browser_dbg-asm.js b/devtools/client/debugger/test/mochitest/browser_dbg-asm.js
index 84308de6f930..751710e75ebc 100644
--- a/devtools/client/debugger/test/mochitest/browser_dbg-asm.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg-asm.js
@@ -10,7 +10,7 @@ add_task(async function() {
   await waitForSources(dbg, "doc-asm.html", "asm.js");
 
   // Make sure sources appear.
-  is(findAllElements(dbg, "sourceNodes").length, 2);
+  is(findAllElements(dbg, "sourceNodes").length, 3);
 
   await selectSource(dbg, "asm.js");
 
diff --git a/devtools/client/debugger/test/mochitest/browser_dbg-content-script-sources.js b/devtools/client/debugger/test/mochitest/browser_dbg-content-script-sources.js
index df5d8fc3b680..23bf2d0ecfb6 100644
--- a/devtools/client/debugger/test/mochitest/browser_dbg-content-script-sources.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg-content-script-sources.js
@@ -49,6 +49,9 @@ add_task(async function() {
   const extension = await installAndStartExtension();
 
   let dbg = await initDebugger("doc-content-script-sources.html");
+  await clickElement(dbg, "sourceDirectoryLabel", 2);
+
+
   await selectContentScriptSources(dbg);
   await closeTab(dbg, "content_script.js");
 
@@ -57,6 +60,9 @@ add_task(async function() {
   await dbg.toolbox.destroy();
   const toolbox = await openToolboxForTab(gBrowser.selectedTab, "jsdebugger");
   dbg = createDebuggerContext(toolbox);
+
+  await clickElement(dbg, "sourceDirectoryLabel", 2);
+
   await selectContentScriptSources(dbg);
 
   await addBreakpoint(dbg, "content_script.js", 2);
diff --git a/devtools/client/debugger/test/mochitest/browser_dbg-sourcemaps.js b/devtools/client/debugger/test/mochitest/browser_dbg-sourcemaps.js
index 3acb76d39285..5aa9c8b41a3b 100644
--- a/devtools/client/debugger/test/mochitest/browser_dbg-sourcemaps.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg-sourcemaps.js
@@ -66,8 +66,8 @@ add_task(async function() {
   const bundleSrc = findSource(dbg, "bundle.js");
 
   // Check that the original sources appear in the source tree
-  await clickElement(dbg, "sourceDirectoryLabel", 3);
-  await assertSourceCount(dbg, 8);
+  await clickElement(dbg, "sourceDirectoryLabel", 4);
+  await assertSourceCount(dbg, 9);
 
   await selectSource(dbg, bundleSrc);
 
diff --git a/devtools/client/debugger/test/mochitest/browser_dbg-sources-arrow-keys.js b/devtools/client/debugger/test/mochitest/browser_dbg-sources-arrow-keys.js
index 286e618f191a..2f3decdab5dc 100644
--- a/devtools/client/debugger/test/mochitest/browser_dbg-sources-arrow-keys.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg-sources-arrow-keys.js
@@ -5,8 +5,8 @@
 add_task(async function() {
   const dbg = await initDebugger("doc-sources.html", "simple1", "simple2", "nested-source", "long.js");
 
-  await clickElement(dbg, "sourceDirectoryLabel", 2);
-  await assertSourceCount(dbg, 7);
+  await clickElement(dbg, "sourceDirectoryLabel", 3);
+  await assertSourceCount(dbg, 8);
 
   // Right key on open dir
   await pressKey(dbg, "Right");
@@ -15,12 +15,12 @@ add_task(async function() {
   // Right key on closed dir
   await pressKey(dbg, "Right");
   await assertSourceCount(dbg, 8);
-  await assertNodeIsFocused(dbg, 3);
+  await assertNodeIsFocused(dbg, 4);
 
   // Left key on a open dir
   await pressKey(dbg, "Left");
-  await assertSourceCount(dbg, 7);
-  await assertNodeIsFocused(dbg, 3);
+  await assertSourceCount(dbg, 8);
+  await assertNodeIsFocused(dbg, 4);
 
   // Down key on a closed dir
   await pressKey(dbg, "Down");
@@ -28,32 +28,33 @@ add_task(async function() {
 
   // Right key on a source
   await pressKey(dbg, "Right");
-  await assertNodeIsFocused(dbg, 5);
+  await assertNodeIsFocused(dbg, 4);
 
   // Down key on a source
+  await waitForSourceCount(dbg, 9);
   await pressKey(dbg, "Down");
-  await assertNodeIsFocused(dbg, 6);
+  await assertNodeIsFocused(dbg, 5);
 
   // Go to bottom of tree and press down key
   await pressKey(dbg, "Down");
   await pressKey(dbg, "Down");
-  await assertNodeIsFocused(dbg, 7);
+  await assertNodeIsFocused(dbg, 6);
 
   // Up key on a source
   await pressKey(dbg, "Up");
-  await assertNodeIsFocused(dbg, 6);
+  await assertNodeIsFocused(dbg, 5);
 
   // Left key on a source
   await pressKey(dbg, "Left");
-  await assertNodeIsFocused(dbg, 2);
+  await assertNodeIsFocused(dbg, 4);
 
   // Left key on a closed dir
   await pressKey(dbg, "Left");
-  await assertSourceCount(dbg, 2);
+  await assertSourceCount(dbg, 8);
   await pressKey(dbg, "Left");
-  await assertNodeIsFocused(dbg, 1);
+  await assertNodeIsFocused(dbg, 3);
 
   // Up Key at the top of the source tree
   await pressKey(dbg, "Up");
-  await assertNodeIsFocused(dbg, 1);
+  await assertNodeIsFocused(dbg, 2);
 });
diff --git a/devtools/client/debugger/test/mochitest/browser_dbg-sources.js b/devtools/client/debugger/test/mochitest/browser_dbg-sources.js
index f6d73bb0b4c5..93941b5afe86 100644
--- a/devtools/client/debugger/test/mochitest/browser_dbg-sources.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg-sources.js
@@ -18,15 +18,15 @@ add_task(async function() {
   } = dbg;
 
   // Expand nodes and make sure more sources appear.
-  await assertSourceCount(dbg, 2);
-  await clickElement(dbg, "sourceDirectoryLabel", 2);
-
-  await assertSourceCount(dbg, 7);
+  await assertSourceCount(dbg, 3);
   await clickElement(dbg, "sourceDirectoryLabel", 3);
+
   await assertSourceCount(dbg, 8);
+  await clickElement(dbg, "sourceDirectoryLabel", 4);
+  await assertSourceCount(dbg, 9);
 
   const selected = waitForDispatch(dbg, "SET_SELECTED_LOCATION");
-  await clickElement(dbg, "sourceNode", 4);
+  await clickElement(dbg, "sourceNode", 5);
   await selected;
   await waitForSelectedSource(dbg);
 
@@ -34,12 +34,12 @@ add_task(async function() {
   await waitForElementWithSelector(dbg, ".sources-list .focused");
 
   const focusedNode = findElementWithSelector(dbg, ".sources-list .focused");
-  const fourthNode = findElement(dbg, "sourceNode", 4);
+  const fourthNode = findElement(dbg, "sourceNode", 5);
   const selectedSource = getSelectedSource().url;
 
   ok(fourthNode.classList.contains("focused"), "4th node is focused");
   ok(selectedSource.includes("nested-source.js"), "nested-source is selected");
-  await assertNodeIsFocused(dbg, 4);
+  await assertNodeIsFocused(dbg, 5);
   await waitForSelectedSource(dbg, "nested-source");
 
   // Make sure new sources appear in the list.
@@ -49,10 +49,10 @@ add_task(async function() {
     content.document.body.appendChild(script);
   });
 
-  await waitForSourceCount(dbg, 9);
-  await assertNodeIsFocused(dbg, 4);
+  await waitForSourceCount(dbg, 10);
+  await assertNodeIsFocused(dbg, 5);
   is(
-    getSourceNodeLabel(dbg, 7),
+    getSourceNodeLabel(dbg, 8),
     "math.min.js",
     "math.min.js - The dynamic script exists"
   );
diff --git a/devtools/client/framework/test/test_browser_toolbox_debugger.js b/devtools/client/framework/test/test_browser_toolbox_debugger.js
index f06f56988677..3512b1dbd2e8 100644
--- a/devtools/client/framework/test/test_browser_toolbox_debugger.js
+++ b/devtools/client/framework/test/test_browser_toolbox_debugger.js
@@ -15,12 +15,11 @@ info(`START: ${new Error().lineNumber}`);
   const document = window.document;
 
   await waitForSources(dbg, testUrl);
-//  yield waitForSourceCount(dbg, 6);
 
   info("Loaded, selecting the test script to debug");
   // First expand the domain
   const domain = [...document.querySelectorAll(".tree-node")].find(node => {
-    return node.textContent.trim() == "mozilla.org";
+    return node.querySelector(".label").textContent.trim() == "mozilla.org";
   });
   const arrow = domain.querySelector(".arrow");
   arrow.click();