diff --git a/background/background.js b/background/background.js
index 57e3e281..7ab9dd6b 100644
--- a/background/background.js
+++ b/background/background.js
@@ -15,7 +15,7 @@ window.API_METHODS = Object.assign(window.API_METHODS || {}, {
   editSave: styleManager.editSave,
 
   getTabUrlPrefix() {
-    return this.sender.tab.url.match(/^([\w-]+:\/\/[^/#]+)/)[1];
+    return this.sender.tab.url.match(/^([\w-]+:\/+[^/#]+)/)[1];
   },
 
   getStyleFromDB: id =>
@@ -254,12 +254,12 @@ if (chrome.contextMenus) {
   createContextMenus(keys);
 }
 
+// reinject content scripts when the extension is reloaded/updated. Firefox
+// would handle this automatically.
 if (!FIREFOX) {
   reinjectContentScripts();
 }
 
-// FIXME: implement exposeIframes in apply.js
-
 // register hotkeys
 if (FIREFOX && browser.commands && browser.commands.update) {
   const hotkeyPrefs = Object.keys(prefs.defaults).filter(k => k.startsWith('hotkey.'));
@@ -305,7 +305,6 @@ function reinjectContentScripts() {
     cs.matches.some(match => {
       if ((match === ALL_URLS || url.match(match)) &&
           (!url.startsWith('chrome') || url === NTP)) {
-        // TODO: add a `msg.pingTab` API?
         msg.sendTab(id, {method: 'ping'})
           .catch(() => false)
           .then(pong => !pong && injectCS(cs, id));
diff --git a/background/style-manager.js b/background/style-manager.js
index f3e47619..653ad29d 100644
--- a/background/style-manager.js
+++ b/background/style-manager.js
@@ -463,7 +463,7 @@ const styleManager = (() => {
   }
 
   function getDomain(url) {
-    return url.match(/^[\w-]+:\/\/(?:[\w:-]+@)?([^:/#]+)/)[1];
+    return url.match(/^[\w-]+:\/+(?:[\w:-]+@)?([^:/#]+)/)[1];
   }
 
   function getUrlNoHash(url) {
diff --git a/background/usercss-helper.js b/background/usercss-helper.js
index d0341d64..572f925c 100644
--- a/background/usercss-helper.js
+++ b/background/usercss-helper.js
@@ -163,7 +163,7 @@
     });
   }
 
-  function install({url, direct, downloaded, tab}, sender) {
+  function install({url, direct, downloaded, tab}, sender = this.sender) {
     tab = tab !== undefined ? tab : sender.tab;
     url = url || tab.url;
     if (direct && !downloaded) {
diff --git a/install-usercss.html b/install-usercss.html
index 9caec3d1..00e71cb8 100644
--- a/install-usercss.html
+++ b/install-usercss.html
@@ -9,6 +9,8 @@
   <link href="global.css" rel="stylesheet">
   <link href="install-usercss/install-usercss.css" rel="stylesheet">
 
+  <script src="js/promisify.js"></script>
+  <script src="js/msg.js"></script>
   <script src="js/messaging.js"></script>
   <script src="js/prefs.js"></script>
   <script src="js/dom.js"></script>
diff --git a/manifest.json b/manifest.json
index 01129353..bf69609a 100644
--- a/manifest.json
+++ b/manifest.json
@@ -68,13 +68,13 @@
       "matches": ["http://userstyles.org/*", "https://userstyles.org/*"],
       "run_at": "document_start",
       "all_frames": true,
-      "js": ["js/promisify.js", "js/msg.js", "content/install-hook-userstyles.js"]
+      "js": ["content/install-hook-userstyles.js"]
     },
     {
       "matches": ["https://openusercss.org/*", "https://openusercss.com/*"],
       "run_at": "document_start",
       "all_frames": false,
-      "js": ["js/promisify.js", "js/msg.js", "content/install-hook-openusercss.js"]
+      "js": ["content/install-hook-openusercss.js"]
     },
     {
       "matches": [
@@ -98,7 +98,7 @@
       ],
       "run_at": "document_idle",
       "all_frames": false,
-      "js": ["js/promisify.js", "js/msg.js", "content/install-hook-usercss.js"]
+      "js": ["content/install-hook-usercss.js"]
     }
   ],
   "browser_action": {