--- a/toolkit/mozapps/extensions/test/xpcshell/head_addons.js
+++ b/toolkit/mozapps/extensions/test/xpcshell/head_addons.js
@@ -63,25 +63,16 @@ ChromeUtils.defineModuleGetter(this, "Mo
                                "resource://testing-common/MockRegistrar.jsm");
 ChromeUtils.defineModuleGetter(this, "MockRegistry",
                                "resource://testing-common/MockRegistry.jsm");
 
 XPCOMUtils.defineLazyServiceGetter(this, "aomStartup",
                                    "@mozilla.org/addons/addon-manager-startup;1",
                                    "amIAddonManagerStartup");
 
-// Whitelist existing tests that still use non-restartless extensions.
-const LEGACY_NON_RESTARTLESS_TESTS = new Set([
-  "test_bug455906.js",
-]);
-
-if (LEGACY_NON_RESTARTLESS_TESTS.has(_TEST_FILE[0].replace(/.*\//, ""))) {
-  Services.prefs.setBoolPref("extensions.legacy.non-restartless.enabled", true);
-}
-
 const {
   awaitPromise,
   createAppInfo,
   createInstallRDF,
   createTempWebExtensionFile,
   createUpdateRDF,
   getFileForAddon,
   manuallyUninstall,

--- a/toolkit/mozapps/extensions/test/xpcshell/test_bug455906.js
+++ b/toolkit/mozapps/extensions/test/xpcshell/test_bug455906.js
@@ -1,21 +1,24 @@
 /* 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/.
  */
 
 const URI_EXTENSION_BLOCKLIST_DIALOG = "chrome://mozapps/content/extensions/blocklist.xul";
 
+ChromeUtils.import("resource://gre/modules/ExtensionUtils.jsm");
 ChromeUtils.import("resource://testing-common/httpd.js");
 ChromeUtils.import("resource://testing-common/MockRegistrar.jsm");
 var gTestserver = new HttpServer();
 gTestserver.start(-1);
 gPort = gTestserver.identity.primaryPort;
 
+const {promiseObserved} = ExtensionUtils;
+
 // register static files with server and interpolate port numbers in them
 mapFile("/data/bug455906_warn.xml", gTestserver);
 mapFile("/data/bug455906_start.xml", gTestserver);
 mapFile("/data/bug455906_block.xml", gTestserver);
 mapFile("/data/bug455906_empty.xml", gTestserver);
 
 // Workaround for Bug 658720 - URL formatter can leak during xpcshell tests
 const PREF_BLOCKLIST_ITEM_URL = "extensions.blocklist.itemURL";
@@ -161,16 +164,17 @@ MockRegistrar.register("@mozilla.org/emb
 function create_addon(addon) {
   var installrdf = "<?xml version=\"1.0\"?>\n" +
                    "\n" +
                    "<RDF xmlns=\"http://www.w3.org/1999/02/22-rdf-syntax-ns#\"\n" +
                    "     xmlns:em=\"http://www.mozilla.org/2004/em-rdf#\">\n" +
                    "  <Description about=\"urn:mozilla:install-manifest\">\n" +
                    "    <em:id>" + addon.id + "</em:id>\n" +
                    "    <em:version>" + addon.version + "</em:version>\n" +
+                   "    <em:bootstrap>true</em:bootstrap>\n" +
                    "    <em:targetApplication>\n" +
                    "      <Description>\n" +
                    "        <em:id>xpcshell@tests.mozilla.org</em:id>\n" +
                    "        <em:minVersion>" + addon.appVersion + "</em:minVersion>\n" +
                    "        <em:maxVersion>" + addon.appVersion + "</em:maxVersion>\n" +
                    "      </Description>\n" +
                    "    </em:targetApplication>\n" +
                    "    <em:name>" + addon.name + "</em:name>\n" +
@@ -366,17 +370,17 @@ function run_test_pt3() {
     gNotificationCheck = check_notification_pt3;
     gTestCheck = check_test_pt3;
     load_blocklist("bug455906_block.xml");
   });
 }
 
 function check_notification_pt3(args) {
   dump("Checking notification pt 3\n");
-  Assert.equal(args.list.length, 6);
+  Assert.equal(args.list.length, 3);
 
   for (let addon of args.list) {
     if (addon.item instanceof Ci.nsIPluginTag) {
       switch (addon.item.name) {
         case "test_bug455906_2":
           Assert.ok(addon.blocked);
           break;
         case "test_bug455906_3":
@@ -441,29 +445,31 @@ function check_test_pt3() {
 
     // Shouldn't be changed
     Assert.equal(check_addon_state(addons[5]), "false,false,true");
     Assert.equal(check_addon_state(addons[6]), "false,false,true");
     Assert.equal(check_plugin_state(PLUGINS[5]), "false,true");
 
     // Back to starting state
     gNotificationCheck = null;
-    gTestCheck = run_test_pt4;
+    gTestCheck = null;
+    promiseObserved("blocklist-updated").then(run_test_pt4);
     load_blocklist("bug455906_start.xml");
   });
 }
 
 function run_test_pt4() {
   AddonManager.getAddonByID(ADDONS[4].id, callback_soon(function(addon) {
     addon.userDisabled = false;
     PLUGINS[4].enabledState = Ci.nsIPluginTag.STATE_ENABLED;
     restartManager();
     check_initial_state(function() {
       gNotificationCheck = check_notification_pt4;
       gTestCheck = check_test_pt4;
+      promiseObserved("blocklist-updated").then(check_test_pt4);
       load_blocklist("bug455906_empty.xml");
     });
   }));
 }
 
 function check_notification_pt4(args) {
   dump("Checking notification pt 4\n");