diff --git a/devtools/client/debugger/new/src/actions/sources/loadSourceText.js b/devtools/client/debugger/new/src/actions/sources/loadSourceText.js
index 9bfb9c79eb86..66c31bbba899 100644
--- a/devtools/client/debugger/new/src/actions/sources/loadSourceText.js
+++ b/devtools/client/debugger/new/src/actions/sources/loadSourceText.js
@@ -5,7 +5,7 @@
 // @flow
 
 import { PROMISE } from "../utils/middleware/promise";
-import { getSource } from "../../selectors";
+import { getSource, getSourcesEpoch } from "../../selectors";
 import { setBreakpointPositions } from "../breakpoints";
 
 import * as parser from "../../workers/parser";
@@ -44,6 +44,7 @@ async function loadSource(state, source: Source, { sourceMaps, client }) {
 
 async function loadSourceTextPromise(
   source: Source,
+  epoch: number,
   { dispatch, getState, client, sourceMaps }: ThunkArgs
 ): Promise<?Source> {
   if (isLoaded(source)) {
@@ -53,6 +54,7 @@ async function loadSourceTextPromise(
   await dispatch({
     type: "LOAD_SOURCE_TEXT",
     sourceId: source.id,
+    epoch,
     [PROMISE]: loadSource(getState(), source, { sourceMaps, client })
   });
 
@@ -82,12 +84,14 @@ export function loadSourceText(inputSource: ?Source) {
     // below in a way that Flow is happy with.
     const source = inputSource;
 
-    const id = source.id;
+    const epoch = getSourcesEpoch(thunkArgs.getState());
+
+    const id = `${epoch}:${source.id}`;
     let promise = requests.get(id);
     if (!promise) {
       promise = (async () => {
         try {
-          return await loadSourceTextPromise(source, thunkArgs);
+          return await loadSourceTextPromise(source, epoch, thunkArgs);
         } catch (e) {
           // TODO: This swallows errors for now. Ideally we would get rid of
           // this once we have a better handle on our async state management.
diff --git a/devtools/client/debugger/new/src/actions/types/SourceAction.js b/devtools/client/debugger/new/src/actions/types/SourceAction.js
index ff20f3c7824d..9704b681353a 100644
--- a/devtools/client/debugger/new/src/actions/types/SourceAction.js
+++ b/devtools/client/debugger/new/src/actions/types/SourceAction.js
@@ -10,7 +10,8 @@ import type { PromiseAction } from "../utils/middleware/promise";
 export type LoadSourceAction = PromiseAction<
   {|
     +type: "LOAD_SOURCE_TEXT",
-    +sourceId: string
+    +sourceId: string,
+    +epoch: number
   |},
   Source
 >;
diff --git a/devtools/client/debugger/new/src/reducers/sources.js b/devtools/client/debugger/new/src/reducers/sources.js
index 57ca8869a198..b152526c8156 100644
--- a/devtools/client/debugger/new/src/reducers/sources.js
+++ b/devtools/client/debugger/new/src/reducers/sources.js
@@ -36,6 +36,8 @@ type DisplayedSources = { [ThreadId]: { [SourceId]: boolean } };
 type GetDisplayedSourcesSelector = OuterState => { [ThreadId]: SourcesMap };
 
 export type SourcesState = {
+  epoch: number,
+
   // All known sources.
   sources: SourcesMap,
 
@@ -63,6 +65,7 @@ const emptySources = {
 export function initialSourcesState(): SourcesState {
   return {
     ...emptySources,
+    epoch: 1,
     selectedLocation: undefined,
     pendingSelectedLocation: prefs.pendingSelectedLocation,
     projectDirectoryRoot: prefs.projectDirectoryRoot,
@@ -164,7 +167,10 @@ function update(
       return updateProjectDirectoryRoot(state, action.url);
 
     case "NAVIGATE":
-      return initialSourcesState();
+      return {
+        ...initialSourcesState(),
+        epoch: state.epoch + 1
+      };
 
     case "SET_FOCUSED_SOURCE_ITEM":
       return { ...state, focusedItem: action.item };
@@ -296,10 +302,19 @@ function updateProjectDirectoryRoot(state: SourcesState, root: string) {
  * Update a source's loaded state fields
  * i.e. loadedState, text, error
  */
-function updateLoadedState(state, action: LoadSourceAction): SourcesState {
+function updateLoadedState(
+  state: SourcesState,
+  action: LoadSourceAction
+): SourcesState {
   const { sourceId } = action;
   let source;
 
+  // If there was a nativation between the time the action was started and
+  // completed, we don't want to update the store.
+  if (action.epoch !== state.epoch) {
+    return state;
+  }
+
   if (action.status === "start") {
     source = { id: sourceId, loadedState: "loading" };
   } else if (action.status === "error") {
@@ -522,6 +537,10 @@ export function getSources(state: OuterState) {
   return state.sources.sources;
 }
 
+export function getSourcesEpoch(state: OuterState) {
+  return state.sources.epoch;
+}
+
 export function getUrls(state: OuterState) {
   return state.sources.urls;
 }