diff --git a/browser/devtools/projecteditor/chrome/content/projecteditor-loader.js b/browser/devtools/projecteditor/chrome/content/projecteditor-loader.js
index 1f626aec6d99..2954d4cb24be 100644
--- a/browser/devtools/projecteditor/chrome/content/projecteditor-loader.js
+++ b/browser/devtools/projecteditor/chrome/content/projecteditor-loader.js
@@ -7,9 +7,9 @@ const promise = require("projecteditor/helpers/promise");
 const ProjectEditor = require("projecteditor/projecteditor");
 
 const SAMPLE_PATH = buildTempDirectoryStructure();
-const SAMPLE_NAME = "DevTools Content";
+const SAMPLE_NAME = "DevTools Content Application Name";
 const SAMPLE_PROJECT_URL = "http://mozilla.org";
-const SAMPLE_ICON = "chrome://browser/skin/devtools/tool-options.svg";
+const SAMPLE_ICON = "chrome://browser/skin/devtools/tool-debugger.svg";
 
 /**
  * Create a workspace for working on projecteditor, available at
@@ -56,11 +56,13 @@ document.addEventListener("DOMContentLoaded", function onDOMReady(e) {
     projecteditor.setProjectToAppPath(SAMPLE_PATH, {
       name: SAMPLE_NAME,
       iconUrl: SAMPLE_ICON,
-      projectOverviewURL: SAMPLE_PROJECT_URL
+      projectOverviewURL: SAMPLE_PROJECT_URL,
+      validationStatus: "valid"
     }).then(() => {
       let allResources = projecteditor.project.allResources();
       console.log("All resources have been loaded", allResources, allResources.map(r=>r.basename).join("|"));
     });
+
   });
 
 }, false);
diff --git a/browser/devtools/projecteditor/chrome/content/projecteditor.xul b/browser/devtools/projecteditor/chrome/content/projecteditor.xul
index 9f5e59d49357..0ab13a74d4f2 100644
--- a/browser/devtools/projecteditor/chrome/content/projecteditor.xul
+++ b/browser/devtools/projecteditor/chrome/content/projecteditor.xul
@@ -4,10 +4,8 @@
    - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
 <?xml-stylesheet href="chrome://browser/skin/devtools/light-theme.css" type="text/css"?>
 <?xml-stylesheet href="chrome://browser/skin/devtools/projecteditor/projecteditor.css" type="text/css"?>
-<?xml-stylesheet href="chrome://browser/content/devtools/widgets.css" type="text/css"?>
 <?xml-stylesheet href="chrome://browser/content/devtools/debugger.css" type="text/css"?>
 <?xml-stylesheet href="chrome://browser/skin/devtools/common.css" type="text/css"?>
-<?xml-stylesheet href="chrome://browser/skin/devtools/widgets.css" type="text/css"?>
 <?xml-stylesheet href="chrome://browser/content/devtools/markup-view.css" type="text/css"?>
 <?xml-stylesheet href="chrome://browser/skin/devtools/markup-view.css" type="text/css"?>
 
diff --git a/browser/devtools/projecteditor/lib/plugins/app-manager/plugin.js b/browser/devtools/projecteditor/lib/plugins/app-manager/plugin.js
index fc79ee3960e3..d3979236de74 100644
--- a/browser/devtools/projecteditor/lib/plugins/app-manager/plugin.js
+++ b/browser/devtools/projecteditor/lib/plugins/app-manager/plugin.js
@@ -5,6 +5,7 @@ const { emit } = require("sdk/event/core");
 const promise = require("projecteditor/helpers/promise");
 var { registerPlugin, Plugin } = require("projecteditor/plugins/core");
 const { AppProjectEditor } = require("./app-project-editor");
+const OPTION_URL = "chrome://browser/skin/devtools/tool-options.svg";
 
 var AppManagerRenderer = Class({
   extends: Plugin,
@@ -25,20 +26,32 @@ var AppManagerRenderer = Class({
     let {appManagerOpts} = this.host.project;
     let doc = elt.ownerDocument;
     let image = doc.createElement("image");
-    let label = doc.createElement("label");
+    let optionImage = doc.createElement("image");
+    let flexElement = doc.createElement("div");
+    let nameLabel = doc.createElement("span");
+    let statusElement = doc.createElement("div");
 
-    label.className = "project-name-label";
     image.className = "project-image";
+    optionImage.className = "project-options";
+    nameLabel.className = "project-name-label";
+    statusElement.className = "project-status";
+    flexElement.className = "project-flex";
 
     let name = appManagerOpts.name || resource.basename;
     let url = appManagerOpts.iconUrl || "icon-sample.png";
+    let status = appManagerOpts.validationStatus || "unknown";
 
-    label.textContent = name;
+    nameLabel.textContent = name;
     image.setAttribute("src", url);
+    optionImage.setAttribute("src", OPTION_URL);
+    statusElement.setAttribute("status", status)
 
     elt.innerHTML = "";
     elt.appendChild(image);
-    elt.appendChild(label);
+    elt.appendChild(nameLabel);
+    elt.appendChild(flexElement);
+    elt.appendChild(statusElement);
+    elt.appendChild(optionImage);
     return true;
   }
 });
diff --git a/browser/devtools/projecteditor/lib/project.js b/browser/devtools/projecteditor/lib/project.js
index 8b19117ae24d..59d0dc513a63 100644
--- a/browser/devtools/projecteditor/lib/project.js
+++ b/browser/devtools/projecteditor/lib/project.js
@@ -136,13 +136,11 @@ var Project = Class({
   /**
    * Get every file path used inside of the project.
    *
-   * @returns generator-iterator<string>
+   * @returns Array<string>
    *          A list of all file paths
    */
-  allPaths: function*() {
-    for (let [path, store] of this.localStores) {
-      yield path;
-    }
+  allPaths: function() {
+    return [path for (path of this.localStores.keys())];
   },
 
   /**
diff --git a/browser/devtools/projecteditor/lib/projecteditor.js b/browser/devtools/projecteditor/lib/projecteditor.js
index 2e3ca9653f86..d0e0efd5742b 100644
--- a/browser/devtools/projecteditor/lib/projecteditor.js
+++ b/browser/devtools/projecteditor/lib/projecteditor.js
@@ -264,14 +264,29 @@ var ProjectEditor = Class({
    * @param string path
    *               The file path to set
    * @param Object opts
-   *               Custom options used by the project. See plugins/app-manager.
+   *               Custom options used by the project.
+   *                - name: display name for project
+   *                - iconUrl: path to icon for project
+   *                - validationStatus: one of 'unknown|error|warning|valid'
+   *                - projectOverviewURL: path to load for iframe when project
+   *                    is selected in the tree.
    * @param Promise
    *        Promise that is resolved once the project is ready to be used.
    */
   setProjectToAppPath: function(path, opts = {}) {
     this.project.appManagerOpts = opts;
-    this.project.removeAllStores();
-    this.project.addPath(path);
+
+    let existingPaths = this.project.allPaths();
+    if (existingPaths.length !== 1 || existingPaths[0] !== path) {
+      // Only fully reset if this is a new path.
+      this.project.removeAllStores();
+      this.project.addPath(path);
+    } else {
+      // Otherwise, just ask for the root to be redrawn
+      let rootResource = this.project.localStores.get(path).root;
+      emit(rootResource, "label-change", rootResource);
+    }
+
     return this.project.refresh();
   },
 
diff --git a/browser/devtools/projecteditor/lib/tree.js b/browser/devtools/projecteditor/lib/tree.js
index 7edeeadd545e..efe2b1a88663 100644
--- a/browser/devtools/projecteditor/lib/tree.js
+++ b/browser/devtools/projecteditor/lib/tree.js
@@ -39,7 +39,7 @@ var ResourceContainer = Class({
 
     this.line = doc.createElementNS(HTML_NS, "div");
     this.line.classList.add("child");
-    this.line.classList.add("side-menu-widget-item");
+    this.line.classList.add("entry");
     this.line.setAttribute("theme", "dark");
     this.line.setAttribute("tabindex", "0");
 
@@ -223,15 +223,14 @@ var TreeView = Class({
     this.models = new Set();
     this.roots = new Set();
     this._containers = new Map();
-    this.elt = document.createElement("vbox");
+    this.elt = document.createElementNS(HTML_NS, "div");
     this.elt.tree = this;
-    this.elt.className = "side-menu-widget-container sources-tree";
+    this.elt.className = "sources-tree";
     this.elt.setAttribute("with-arrows", "true");
     this.elt.setAttribute("theme", "dark");
     this.elt.setAttribute("flex", "1");
 
     this.children = document.createElementNS(HTML_NS, "ul");
-    this.children.setAttribute("flex", "1");
     this.elt.appendChild(this.children);
 
     this.resourceChildrenChanged = this.resourceChildrenChanged.bind(this);
@@ -315,7 +314,7 @@ var TreeView = Class({
         return;
       }
       let container = this.importResource(root);
-      container.line.classList.add("side-menu-widget-group-title");
+      container.line.classList.add("entry-group-title");
       container.line.setAttribute("theme", "dark");
       this.selectContainer(container);
 
diff --git a/browser/devtools/projecteditor/test/browser.ini b/browser/devtools/projecteditor/test/browser.ini
index 965ff56493e3..a39efe1e5e4e 100644
--- a/browser/devtools/projecteditor/test/browser.ini
+++ b/browser/devtools/projecteditor/test/browser.ini
@@ -5,6 +5,7 @@ support-files =
   head.js
   helper_homepage.html
 
+[browser_projecteditor_app_options.js]
 [browser_projecteditor_delete_file.js]
 [browser_projecteditor_editing_01.js]
 [browser_projecteditor_immediate_destroy.js]
diff --git a/browser/devtools/projecteditor/test/browser_projecteditor_app_options.js b/browser/devtools/projecteditor/test/browser_projecteditor_app_options.js
new file mode 100644
index 000000000000..2141c19b033b
--- /dev/null
+++ b/browser/devtools/projecteditor/test/browser_projecteditor_app_options.js
@@ -0,0 +1,102 @@
+/* vim: set ts=2 et sw=2 tw=80: */
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that options can be changed without resetting the whole
+// editor.
+let test = asyncTest(function*() {
+
+  let TEMP_PATH = buildTempDirectoryStructure();
+  let projecteditor = yield addProjectEditorTab();
+
+  let resourceBeenAdded = promise.defer();
+  projecteditor.project.once("resource-added", () => {
+    info ("A resource has been added");
+    resourceBeenAdded.resolve();
+  });
+
+  info ("About to set project to: " + TEMP_PATH);
+  yield projecteditor.setProjectToAppPath(TEMP_PATH, {
+    name: "Test",
+    iconUrl: "chrome://browser/skin/devtools/tool-options.svg",
+    projectOverviewURL: SAMPLE_WEBAPP_URL
+  });
+
+  info ("Making sure a resource has been added before continuing");
+  yield resourceBeenAdded.promise;
+
+  info ("From now on, if a resource is added it should fail");
+  projecteditor.project.on("resource-added", failIfResourceAdded);
+
+  info ("Getting ahold and validating the project header DOM");
+  let header = projecteditor.document.querySelector(".entry-group-title");
+  let image = header.querySelector(".project-image");
+  let nameLabel = header.querySelector(".project-name-label");
+  let statusElement = header.querySelector(".project-status");
+  is (statusElement.getAttribute("status"), "unknown", "The status starts out as unknown.");
+  is (nameLabel.textContent, "Test", "The name label has been set correctly");
+  is (image.getAttribute("src"), "chrome://browser/skin/devtools/tool-options.svg", "The icon has been set correctly");
+
+  info ("About to set project with new options.");
+  yield projecteditor.setProjectToAppPath(TEMP_PATH, {
+    name: "Test2",
+    iconUrl: "chrome://browser/skin/devtools/tool-inspector.svg",
+    projectOverviewURL: SAMPLE_WEBAPP_URL,
+    validationStatus: "error"
+  });
+
+  ok (!nameLabel.parentNode, "The old elements have been removed");
+
+  info ("Getting ahold of and validating the project header DOM");
+  let image = header.querySelector(".project-image");
+  let nameLabel = header.querySelector(".project-name-label");
+  let statusElement = header.querySelector(".project-status");
+  is (statusElement.getAttribute("status"), "error", "The status has been set correctly.");
+  is (nameLabel.textContent, "Test2", "The name label has been set correctly");
+  is (image.getAttribute("src"), "chrome://browser/skin/devtools/tool-inspector.svg", "The icon has been set correctly");
+
+  info ("About to set project with new options.");
+  yield projecteditor.setProjectToAppPath(TEMP_PATH, {
+    name: "Test3",
+    iconUrl: "chrome://browser/skin/devtools/tool-webconsole.svg",
+    projectOverviewURL: SAMPLE_WEBAPP_URL,
+    validationStatus: "warning"
+  });
+
+  ok (!nameLabel.parentNode, "The old elements have been removed");
+
+  info ("Getting ahold of and validating the project header DOM");
+  let image = header.querySelector(".project-image");
+  let nameLabel = header.querySelector(".project-name-label");
+  let statusElement = header.querySelector(".project-status");
+  is (statusElement.getAttribute("status"), "warning", "The status has been set correctly.");
+  is (nameLabel.textContent, "Test3", "The name label has been set correctly");
+  is (image.getAttribute("src"), "chrome://browser/skin/devtools/tool-webconsole.svg", "The icon has been set correctly");
+
+  info ("About to set project with new options.");
+  yield projecteditor.setProjectToAppPath(TEMP_PATH, {
+    name: "Test4",
+    iconUrl: "chrome://browser/skin/devtools/tool-debugger.svg",
+    projectOverviewURL: SAMPLE_WEBAPP_URL,
+    validationStatus: "valid"
+  });
+
+  ok (!nameLabel.parentNode, "The old elements have been removed");
+
+  info ("Getting ahold of and validating the project header DOM");
+  let image = header.querySelector(".project-image");
+  let nameLabel = header.querySelector(".project-name-label");
+  let statusElement = header.querySelector(".project-status");
+  is (statusElement.getAttribute("status"), "valid", "The status has been set correctly.");
+  is (nameLabel.textContent, "Test4", "The name label has been set correctly");
+  is (image.getAttribute("src"), "chrome://browser/skin/devtools/tool-debugger.svg", "The icon has been set correctly");
+
+  info ("Test finished, cleaning up");
+  projecteditor.project.off("resource-added", failIfResourceAdded);
+});
+
+function failIfResourceAdded() {
+  ok (false, "A resource has been added, but it shouldn't have been");
+}
diff --git a/browser/devtools/projecteditor/test/browser_projecteditor_editing_01.js b/browser/devtools/projecteditor/test/browser_projecteditor_editing_01.js
index db8b5e2591b7..b31d446012c7 100644
--- a/browser/devtools/projecteditor/test/browser_projecteditor_editing_01.js
+++ b/browser/devtools/projecteditor/test/browser_projecteditor_editing_01.js
@@ -7,7 +7,7 @@
 // Test ProjectEditor basic functionality
 let test = asyncTest(function*() {
   let projecteditor = yield addProjectEditorTabForTempDirectory();
-  let TEMP_PATH = [...projecteditor.project.allPaths()][0];
+  let TEMP_PATH = projecteditor.project.allPaths()[0];
 
   is (getTempFile("").path, TEMP_PATH, "Temp path is set correctly.");
 
diff --git a/browser/devtools/projecteditor/test/browser_projecteditor_stores.js b/browser/devtools/projecteditor/test/browser_projecteditor_stores.js
index 08b356af73f3..8c375ea83786 100644
--- a/browser/devtools/projecteditor/test/browser_projecteditor_stores.js
+++ b/browser/devtools/projecteditor/test/browser_projecteditor_stores.js
@@ -7,10 +7,10 @@
 // Test ProjectEditor basic functionality
 let test = asyncTest(function*() {
   let projecteditor = yield addProjectEditorTabForTempDirectory();
-  let TEMP_PATH = [...projecteditor.project.allPaths()][0];
+  let TEMP_PATH = projecteditor.project.allPaths()[0];
   is (getTempFile("").path, TEMP_PATH, "Temp path is set correctly.");
 
-  is ([...projecteditor.project.allPaths()].length, 1, "1 path is set");
+  is (projecteditor.project.allPaths().length, 1, "1 path is set");
   projecteditor.project.removeAllStores();
-  is ([...projecteditor.project.allPaths()].length, 0, "No paths are remaining");
+  is (projecteditor.project.allPaths().length, 0, "No paths are remaining");
 });
diff --git a/browser/devtools/projecteditor/test/browser_projecteditor_tree_selection.js b/browser/devtools/projecteditor/test/browser_projecteditor_tree_selection.js
index 3835fab0b724..9d23c9793545 100644
--- a/browser/devtools/projecteditor/test/browser_projecteditor_tree_selection.js
+++ b/browser/devtools/projecteditor/test/browser_projecteditor_tree_selection.js
@@ -8,7 +8,7 @@
 
 let test = asyncTest(function*() {
   let projecteditor = yield addProjectEditorTabForTempDirectory();
-  let TEMP_PATH = [...projecteditor.project.allPaths()][0];
+  let TEMP_PATH = projecteditor.project.allPaths()[0];
 
   is (getTempFile("").path, TEMP_PATH, "Temp path is set correctly.");
 
diff --git a/browser/themes/shared/devtools/projecteditor/projecteditor.css b/browser/themes/shared/devtools/projecteditor/projecteditor.css
index 1d11f603bbe8..6fa7fd43e03c 100644
--- a/browser/themes/shared/devtools/projecteditor/projecteditor.css
+++ b/browser/themes/shared/devtools/projecteditor/projecteditor.css
@@ -11,6 +11,20 @@
   display: none;
 }
 
+.arrow {
+  -moz-appearance: treetwisty;
+  width: 20px;
+  height: 20px;
+}
+
+.arrow[open] {
+  -moz-appearance: treetwistyopen;
+}
+
+.arrow[invisible] {
+  visibility: hidden;
+}
+
 #projecteditor-menubar {
   /* XXX: Hide menu bar until we have option to add menu items
      to an existing one. */
@@ -27,7 +41,13 @@
 
 .sources-tree {
   overflow:auto;
+  overflow-x: hidden;
   -moz-user-focus: normal;
+
+  /* Allows this to expand inside of parent xul element, while
+     still supporting child flexbox elements, including ellipses. */
+  -moz-box-flex: 1;
+  display: block;
 }
 
 .sources-tree input {
@@ -37,94 +57,95 @@
 
 #main-deck .sources-tree {
   background: rgb(225, 225, 225);
-  min-width: 50px;
+  min-width: 100px;
 }
 
-#main-deck .sources-tree .side-menu-widget-item {
+.entry {
   color: #18191A;
+  display: flex;
+  align-items: center;
 }
 
-#main-deck .sources-tree .side-menu-widget-item .file-label {
-  vertical-align: middle;
-  display: inline-block;
+.entry .file-label {
+  display: flex;
+  flex: 1;
+  align-items: center;
 }
 
-#main-deck .sources-tree .side-menu-widget-item .file-icon {
+.entry .file-icon {
   display: inline-block;
   background: url(file-icons-sheet@2x.png);
   background-size: 140px 15px;
   background-repeat: no-repeat;
   width: 20px;
   height: 15px;
-  vertical-align: middle;
   background-position: -40px 0;
+  flex-shrink: 0;
 }
 
-#main-deck .sources-tree .side-menu-widget-item .file-icon.icon-none {
+.entry .file-icon.icon-none {
   display: none;
 }
 
-#main-deck .sources-tree .side-menu-widget-item .icon-css {
+.entry .icon-css {
   background-position: 0 0;
 }
 
-#main-deck .sources-tree .side-menu-widget-item .icon-js {
+.entry .icon-js {
   background-position: -20px 0;
 }
 
-#main-deck .sources-tree .side-menu-widget-item .icon-html {
+.entry .icon-html {
   background-position: -40px 0;
 }
 
-#main-deck .sources-tree .side-menu-widget-item .icon-file {
+.entry .icon-file {
   background-position: -60px 0;
 }
 
-#main-deck .sources-tree .side-menu-widget-item .icon-folder {
+.entry .icon-folder {
   background-position: -80px 0;
 }
 
-#main-deck .sources-tree .side-menu-widget-item .icon-img {
+.entry .icon-img {
   background-position: -100px 0;
 }
 
-#main-deck .sources-tree .side-menu-widget-item .icon-manifest {
+.entry .icon-manifest {
   background-position: -120px 0;
 }
 
-#main-deck .sources-tree .side-menu-widget-item:hover {
-  background: rgba(0, 0, 0, .05);
+.entry {
+  border: none;
+  box-shadow: none;
+  white-space: nowrap;
   cursor: pointer;
 }
 
-#main-deck .sources-tree .side-menu-widget-item {
-  border: none;
-  box-shadow: none;
-  line-height: 20px;
-  vertical-align: middle;
-  white-space: nowrap;
+.entry:hover:not(.entry-group-title):not(.selected) {
+  background: rgba(0, 0, 0, .05);
 }
 
-#main-deck .sources-tree .side-menu-widget-item.selected {
-  background: #3875D7;
+.entry.selected {
+  background: rgba(56, 117, 215, 1);
   color: #F5F7FA;
   outline: none;
 }
 
-#main-deck .sources-tree .side-menu-widget-group-title,
-#main-deck .sources-tree .side-menu-widget-group-title:hover:not(.selected) {
-  background: #B4D7EB;
-  color: #222;
+.entry-group-title {
+  background: rgba(56, 117, 215, 0.8);
+  color: #F5F7FA;
   font-weight: bold;
   font-size: 1.05em;
-  cursor: default;
   line-height: 35px;
+  padding: 0 10px;
 }
 
-#main-deck .sources-tree li.child:only-child .side-menu-widget-group-title .expander {
+.sources-tree .entry-group-title .expander {
   display: none;
 }
-#main-deck .sources-tree .side-menu-widget-item .expander {
+
+.entry .expander {
   width: 16px;
   padding: 0;
 }
@@ -143,30 +164,62 @@
   padding: 0 3px;
 }
 
+/* App Manager */
 .project-name-label {
   font-weight: bold;
   padding-left: 10px;
+  overflow: hidden;
+  text-overflow: ellipsis;
 }
 
-.project-version-label {
-  color: #666;
-  padding-left: 5px;
-  font-size: .9em;
+.project-flex {
+  flex: 1;
 }
 
 .project-image {
-  max-height: 28px;
-  margin-left: -.5em;
-  vertical-align: middle;
+  max-height: 25px;
+  margin-left: -10px;
 }
 
-.editor-image {
-  padding: 10px;
+.project-image,
+.project-status,
+.project-options {
+  flex-shrink: 0;
 }
 
+.project-status {
+  width: 10px;
+  height: 10px;
+  border-radius: 50%;
+  border: solid 1px rgba(255, 255, 255, .5);
+  margin-right: 10px;
+  visibility: hidden;
+}
+
+.project-status[status=valid] {
+  background: #70bf53;
+  visibility: visible;
+}
+
+.project-status[status=warning] {
+  background: #d99b28;
+  visibility: visible;
+}
+
+.project-status[status=error] {
+  background: #ed2655;
+  visibility: visible;
+}
+
+/* Status Bar */
 .projecteditor-file-label {
   font-weight: bold;
   padding-left: 29px;
-  vertical-align: middle;
+  padding-right: 10px;
+  flex: 1;
 }
 
+/* Image View */
+.editor-image {
+  padding: 10px;
+}