diff --git a/devtools/client/aboutdebugging-new/src/actions/runtime.js b/devtools/client/aboutdebugging-new/src/actions/runtime.js
index 936a62d8a68e..1a901d89b79d 100644
--- a/devtools/client/aboutdebugging-new/src/actions/runtime.js
+++ b/devtools/client/aboutdebugging-new/src/actions/runtime.js
@@ -5,13 +5,16 @@
 "use strict";
 
 const { AddonManager } = require("resource://gre/modules/AddonManager.jsm");
-const { BrowserToolboxProcess } =
-  require("resource://devtools/client/framework/ToolboxProcess.jsm");
-const { Cc, Ci } = require("chrome");
 const { DebuggerClient } = require("devtools/shared/client/debugger-client");
 const { DebuggerServer } = require("devtools/server/main");
 const { gDevToolsBrowser } = require("devtools/client/framework/devtools-browser");
 
+const {
+  debugLocalAddon,
+  openTemporaryExtension,
+  uninstallAddon,
+} = require("devtools/client/aboutdebugging/modules/addon");
+
 const {
   CONNECT_RUNTIME_FAILURE,
   CONNECT_RUNTIME_START,
@@ -31,8 +34,6 @@ const {
   REQUEST_WORKERS_SUCCESS,
 } = require("../constants");
 
-let browserToolboxProcess = null;
-
 function connectRuntime() {
   return async (dispatch, getState) => {
     dispatch({ type: CONNECT_RUNTIME_START });
@@ -80,17 +81,7 @@ function inspectDebugTarget(type, id) {
         break;
       }
       case DEBUG_TARGETS.EXTENSION: {
-        // Close current debugging toolbox and open a new one.
-        if (browserToolboxProcess) {
-          browserToolboxProcess.close();
-        }
-
-        browserToolboxProcess = BrowserToolboxProcess.init({
-          addonID: id,
-          onClose: () => {
-            browserToolboxProcess = null;
-          }
-        });
+        debugLocalAddon(id);
         break;
       }
       case DEBUG_TARGETS.WORKER: {
@@ -108,30 +99,15 @@ function inspectDebugTarget(type, id) {
 }
 
 function installTemporaryExtension() {
-  const fp = Cc["@mozilla.org/filepicker;1"].createInstance(Ci.nsIFilePicker);
-  fp.init(window, "Select Manifest File or Package (.xpi)", Ci.nsIFilePicker.modeOpen);
-  fp.open(async res => {
-    if (res == Ci.nsIFilePicker.returnCancel || !fp.file) {
-      return;
-    }
-
-    let file = fp.file;
-
-    // AddonManager.installTemporaryAddon accepts either
-    // addon directory or final xpi file.
-    if (!file.isDirectory() &&
-        !file.leafName.endsWith(".xpi") && !file.leafName.endsWith(".zip")) {
-      file = file.parent;
-    }
-
+  return async (dispatch, getState) => {
+    const message = "Select Manifest File or Package (.xpi)";
+    const file = await openTemporaryExtension(window, message);
     try {
       await AddonManager.installTemporaryAddon(file);
     } catch (e) {
       console.error(e);
     }
-  });
-
-  return () => {};
+  };
 }
 
 function pushServiceWorker(actor) {
@@ -161,11 +137,7 @@ function reloadTemporaryExtension(actor) {
 function removeTemporaryExtension(id) {
   return async () => {
     try {
-      const addon = await AddonManager.getAddonByID(id);
-
-      if (addon) {
-        await addon.uninstall();
-      }
+      await uninstallAddon(id);
     } catch (e) {
       console.error(e);
     }
diff --git a/devtools/client/aboutdebugging-new/src/middleware/extension-component-data.js b/devtools/client/aboutdebugging-new/src/middleware/extension-component-data.js
index 45b1f1572ef7..0461a105abc1 100644
--- a/devtools/client/aboutdebugging-new/src/middleware/extension-component-data.js
+++ b/devtools/client/aboutdebugging-new/src/middleware/extension-component-data.js
@@ -9,6 +9,11 @@ const {
   REQUEST_EXTENSIONS_SUCCESS,
 } = require("../constants");
 
+const {
+  getExtensionUuid,
+  parseFileUri
+} = require("devtools/client/aboutdebugging/modules/addon");
+
 /**
  * This middleware converts extensions object that get from DebuggerClient.listAddons()
  * to data which is used in DebugTargetItem.
@@ -33,16 +38,7 @@ function getFilePath(extension) {
     return null;
   }
 
-  // Strip a leading slash from Windows drive letter URIs.
-  // file:///home/foo ~> /home/foo
-  // file:///C:/foo ~> C:/foo
-  const windowsRegex = /^file:\/\/\/([a-zA-Z]:\/.*)/;
-
-  if (windowsRegex.test(extension.url)) {
-    return windowsRegex.exec(extension.url)[1];
-  }
-
-  return extension.url.slice("file://".length);
+  return parseFileUri(extension.url);
 }
 
 function toComponentData(extensions) {
@@ -51,7 +47,7 @@ function toComponentData(extensions) {
     const { actor, iconURL, id, manifestURL, name } = extension;
     const icon = iconURL || "chrome://mozapps/skin/extensions/extensionGeneric.svg";
     const location = getFilePath(extension);
-    const uuid = manifestURL ? /moz-extension:\/\/([^/]*)/.exec(manifestURL)[1] : null;
+    const uuid = getExtensionUuid(extension);
     return {
       name,
       icon,
diff --git a/devtools/client/aboutdebugging/components/addons/Controls.js b/devtools/client/aboutdebugging/components/addons/Controls.js
index db02eece50bd..6a90e6c07159 100644
--- a/devtools/client/aboutdebugging/components/addons/Controls.js
+++ b/devtools/client/aboutdebugging/components/addons/Controls.js
@@ -10,10 +10,10 @@
 loader.lazyImporter(this, "AddonManager",
   "resource://gre/modules/AddonManager.jsm");
 
-const { Cc, Ci } = require("chrome");
 const { createFactory, Component } = require("devtools/client/shared/vendor/react");
 const PropTypes = require("devtools/client/shared/vendor/react-prop-types");
 const dom = require("devtools/client/shared/vendor/react-dom-factories");
+const { openTemporaryExtension } = require("devtools/client/aboutdebugging/modules/addon");
 const Services = require("Services");
 const AddonsInstallError = createFactory(require("./InstallError"));
 
@@ -49,26 +49,10 @@ class AddonsControls extends Component {
     Services.prefs.setBoolPref("devtools.debugger.remote-enabled", enabled);
   }
 
-  loadAddonFromFile() {
-    this.setState({ installError: null });
-    const fp = Cc["@mozilla.org/filepicker;1"].createInstance(Ci.nsIFilePicker);
-    fp.init(window,
-      Strings.GetStringFromName("selectAddonFromFile2"),
-      Ci.nsIFilePicker.modeOpen);
-    fp.open(res => {
-      if (res == Ci.nsIFilePicker.returnCancel || !fp.file) {
-        return;
-      }
-      let file = fp.file;
-      // AddonManager.installTemporaryAddon accepts either
-      // addon directory or final xpi file.
-      if (!file.isDirectory() &&
-          !file.leafName.endsWith(".xpi") && !file.leafName.endsWith(".zip")) {
-        file = file.parent;
-      }
-
-      this.installAddon(file);
-    });
+  async loadAddonFromFile() {
+    const message = Strings.GetStringFromName("selectAddonFromFile2");
+    const file = await openTemporaryExtension(window, message);
+    this.installAddon(file);
   }
 
   retryInstall() {
diff --git a/devtools/client/aboutdebugging/components/addons/Target.js b/devtools/client/aboutdebugging/components/addons/Target.js
index c3f46550c84e..8522d4b9f7d7 100644
--- a/devtools/client/aboutdebugging/components/addons/Target.js
+++ b/devtools/client/aboutdebugging/components/addons/Target.js
@@ -12,6 +12,7 @@ const dom = require("devtools/client/shared/vendor/react-dom-factories");
 const {
   debugLocalAddon,
   debugRemoteAddon,
+  getExtensionUuid,
   isLegacyTemporaryExtension,
   isTemporaryID,
   parseFileUri,
@@ -65,11 +66,11 @@ function addonIDforTarget(target) {
 }
 
 function internalIDForTarget(target) {
-  if (!target.manifestURL) {
+  const uuid = getExtensionUuid(target);
+  if (!uuid) {
     return [];
   }
-  // Strip off the protocol and rest, leaving us with just the UUID.
-  const uuid = /moz-extension:\/\/([^/]*)/.exec(target.manifestURL)[1];
+
   return [
     dom.dt(
       { className: "addon-target-info-label" },
diff --git a/devtools/client/aboutdebugging/modules/addon.js b/devtools/client/aboutdebugging/modules/addon.js
index 31dc19734798..67f881eb6ac4 100644
--- a/devtools/client/aboutdebugging/modules/addon.js
+++ b/devtools/client/aboutdebugging/modules/addon.js
@@ -4,6 +4,7 @@
 
 "use strict";
 
+const { Cc, Ci } = require("chrome");
 loader.lazyImporter(this, "BrowserToolboxProcess",
   "resource://devtools/client/framework/ToolboxProcess.jsm");
 loader.lazyImporter(this, "AddonManager", "resource://gre/modules/AddonManager.jsm");
@@ -72,6 +73,10 @@ exports.debugRemoteAddon = async function(addonForm, client) {
   });
 };
 
+/**
+ * Uninstall the addon with the provided id.
+ * Resolves when the addon shutdown has completed.
+ */
 exports.uninstallAddon = async function(addonID) {
   const addon = await AddonManager.getAddonByID(addonID);
   return addon && addon.uninstall();
@@ -104,3 +109,47 @@ exports.parseFileUri = function(url) {
   }
   return url.slice("file://".length);
 };
+
+exports.getExtensionUuid = function(extension) {
+  const { manifestURL } = extension;
+  // Strip off the protocol and rest, leaving us with just the UUID.
+  return manifestURL ? /moz-extension:\/\/([^/]*)/.exec(manifestURL)[1] : null;
+};
+
+/**
+ * Open a file picker to allow the user to locate a temporary extension. A temporary
+ * extension can either be:
+ * - a folder
+ * - a .xpi file
+ * - a .zip file
+ *
+ * @param  {Window} win
+ *         The window object where the filepicker should be opened.
+ *         Note: We cannot use the global window object here because it is undefined if
+ *         this module is loaded from a file outside of devtools/client/aboutdebugging/.
+ *         See browser-loader.js `uri.startsWith(baseURI)` for more details.
+ * @param  {String} message
+ *         The help message that should be displayed to the user in the filepicker.
+ * @return {Promise} returns a promise that resolves a File object corresponding to the
+ *         file selected by the user.
+ */
+exports.openTemporaryExtension = function(win, message) {
+  return new Promise(resolve => {
+    const fp = Cc["@mozilla.org/filepicker;1"].createInstance(Ci.nsIFilePicker);
+    fp.init(win, message, Ci.nsIFilePicker.modeOpen);
+    fp.open(res => {
+      if (res == Ci.nsIFilePicker.returnCancel || !fp.file) {
+        return;
+      }
+      let file = fp.file;
+      // AddonManager.installTemporaryAddon accepts either
+      // addon directory or final xpi file.
+      if (!file.isDirectory() &&
+          !file.leafName.endsWith(".xpi") && !file.leafName.endsWith(".zip")) {
+        file = file.parent;
+      }
+
+      resolve(file);
+    });
+  });
+};