--- a/toolkit/components/extensions/ExtensionXPCShellUtils.jsm
+++ b/toolkit/components/extensions/ExtensionXPCShellUtils.jsm
@@ -425,26 +425,21 @@ class ExtensionWrapper {
 
   onMessage(msg, callback) {
     this.checkDuplicateListeners(msg);
     this.messageHandler.set(msg, callback);
   }
 }
 
 class AOMExtensionWrapper extends ExtensionWrapper {
-  constructor(testScope, xpiFile, installType) {
+  constructor(testScope) {
     super(testScope);
 
     this.onEvent = this.onEvent.bind(this);
 
-    this.file = xpiFile;
-    this.installType = installType;
-
-    this.cleanupFiles = [xpiFile];
-
     Management.on("ready", this.onEvent);
     Management.on("shutdown", this.onEvent);
     Management.on("startup", this.onEvent);
 
     AddonTestUtils.on("addon-manager-shutdown", this.onEvent);
     AddonTestUtils.on("addon-manager-started", this.onEvent);
 
     AddonManager.addAddonListener(this);
@@ -457,33 +452,16 @@ class AOMExtensionWrapper extends Extens
     Management.off("ready", this.onEvent);
     Management.off("shutdown", this.onEvent);
     Management.off("startup", this.onEvent);
 
     AddonTestUtils.off("addon-manager-shutdown", this.onEvent);
     AddonTestUtils.off("addon-manager-started", this.onEvent);
 
     AddonManager.removeAddonListener(this);
-
-    for (let file of this.cleanupFiles.splice(0)) {
-      try {
-        Services.obs.notifyObservers(file, "flush-cache-entry");
-        file.remove(false);
-      } catch (e) {
-        Cu.reportError(e);
-      }
-    }
-  }
-
-  maybeSetID(uri, id) {
-    if (!this.id && uri instanceof Ci.nsIJARURI &&
-        uri.JARFile.QueryInterface(Ci.nsIFileURL)
-           .file.equals(this.file)) {
-      this.id = id;
-    }
   }
 
   setRestarting() {
     if (this.state !== "restarting") {
       this.startupPromise = new Promise(resolve => {
         this.resolveStartup = resolve;
       }).then(async result => {
         await this.addonPromise;
@@ -556,16 +534,79 @@ class AOMExtensionWrapper extends Extens
           this.state = "running";
           this.resolveStartup(extension);
         }
         break;
       }
     }
   }
 
+  async _flushCache() {
+    if (this.extension && this.extension.rootURI instanceof Ci.nsIJARURI) {
+      let file = this.extension.rootURI.JARFile.QueryInterface(Ci.nsIFileURL).file;
+      await Services.ppmm.broadcastAsyncMessage("Extension:FlushJarCache", {path: file.path});
+    }
+  }
+
+  get version() {
+    return this.addon && this.addon.version;
+  }
+
+  async unload() {
+    await this._flushCache();
+    return super.unload();
+  }
+
+  async upgrade(data) {
+    this.startupPromise = new Promise(resolve => {
+      this.resolveStartup = resolve;
+    });
+    this.state = "restarting";
+
+    await this._flushCache();
+
+    let xpiFile = Extension.generateXPI(data);
+
+    this.cleanupFiles.push(xpiFile);
+
+    return this._install(xpiFile);
+  }
+}
+
+class InstallableWrapper extends AOMExtensionWrapper {
+  constructor(testScope, xpiFile, installType) {
+    super(testScope);
+
+    this.file = xpiFile;
+    this.installType = installType;
+
+    this.cleanupFiles = [xpiFile];
+  }
+
+  destroy() {
+    super.destroy();
+
+    for (let file of this.cleanupFiles.splice(0)) {
+      try {
+        Services.obs.notifyObservers(file, "flush-cache-entry");
+        file.remove(false);
+      } catch (e) {
+        Cu.reportError(e);
+      }
+    }
+  }
+
+  maybeSetID(uri, id) {
+    if (!this.id && uri instanceof Ci.nsIJARURI &&
+        uri.JARFile.QueryInterface(Ci.nsIFileURL)
+           .file.equals(this.file)) {
+      this.id = id;
+    }
+  }
+
   _install(xpiFile) {
     if (this.installType === "temporary") {
       return AddonManager.installTemporaryAddon(xpiFile).then(addon => {
         this.id = addon.id;
         this.addon = addon;
 
         return this.startupPromise;
       }).catch(e => {
@@ -588,59 +629,43 @@ class AOMExtensionWrapper extends Extens
         install.addListener(listener);
         install.install();
 
         return this.startupPromise;
       });
     }
   }
 
-  async _flushCache() {
-    if (this.extension && this.extension.rootURI instanceof Ci.nsIJARURI) {
-      let file = this.extension.rootURI.JARFile.QueryInterface(Ci.nsIFileURL).file;
-      await Services.ppmm.broadcastAsyncMessage("Extension:FlushJarCache", {path: file.path});
-    }
-  }
-
-  get version() {
-    return this.addon && this.addon.version;
-  }
-
   startup() {
     if (this.state != "uninitialized") {
       throw new Error("Extension already started");
     }
 
     this.state = "pending";
     this.startupPromise = new Promise(resolve => {
       this.resolveStartup = resolve;
     });
 
     return this._install(this.file);
   }
+}
 
-  async unload() {
-    await this._flushCache();
-    return super.unload();
-  }
+class ExternallyInstalledWrapper extends AOMExtensionWrapper {
+  constructor(testScope, id) {
+    super(testScope);
 
-  async upgrade(data) {
+    this.id = id;
     this.startupPromise = new Promise(resolve => {
       this.resolveStartup = resolve;
     });
-    this.state = "restarting";
-
-    await this._flushCache();
 
-    let xpiFile = Extension.generateXPI(data);
+    this.state = "restarting";
+  }
 
-    this.cleanupFiles.push(xpiFile);
-
-    return this._install(xpiFile);
-  }
+  maybeSetID(uri, id) { }
 }
 
 var ExtensionTestUtils = {
   BASE_MANIFEST,
 
   async normalizeManifest(manifest, manifestType = "manifest.WebExtensionManifest",
                           baseManifest = BASE_MANIFEST) {
     await Management.lazyInit();
@@ -749,17 +774,23 @@ var ExtensionTestUtils = {
     }
 
     let extension = Extension.generate(data);
 
     return new ExtensionWrapper(this.currentScope, extension);
   },
 
   loadExtensionXPI(xpiFile, useAddonManager = "temporary") {
-    return new AOMExtensionWrapper(this.currentScope, xpiFile, useAddonManager);
+    return new InstallableWrapper(this.currentScope, xpiFile, useAddonManager);
+  },
+
+  // Create a wrapper for a webextension that will be installed
+  // by some external process (e.g., Normandy)
+  expectExtension(id) {
+    return new ExternallyInstalledWrapper(this.currentScope, id);
   },
 
   get remoteContentScripts() {
     return REMOTE_CONTENT_SCRIPTS;
   },
 
   set remoteContentScripts(val) {
     REMOTE_CONTENT_SCRIPTS = !!val;