Issue 6777 - Clicking Subscribe link on testpages.adblockplus.org works only the second time

lib/options.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 26 matching lines @@
     // starting with Firefox 56 an extension can query for its own URLs:
     // https://bugzilla.mozilla.org/show_bug.cgi?id=1271354
     let fullOptionsUrl = browser.extension.getURL(optionsUrl);
     let optionsTab = tabs.find(tab => tab.url == fullOptionsUrl);
     if (optionsTab)
     {
       callback(optionsTab);
       return;
     }
 
-    // Newly created tabs might have about:blank as their URL in Firefox rather
-    // than the final options page URL, we need to wait for those to finish
-    // loading.
+    // Newly created tabs might have about:blank as their URL in Firefox
+    // or undefined in Microsoft Edge rather than the final options page URL,
+    // we need to wait for those to finish loading.
     let potentialOptionTabIds = new Set(
-      tabs.filter(tab => tab.url == "about:blank" && tab.status == "loading")
+      tabs.filter(tab =>
+            (tab.url == "about:blank" || !tab.url) && tab.status == "loading")
           .map(tab => tab.id)
     );
     if (potentialOptionTabIds.size == 0)
     {
       callback();
       return;
     }
     let removeListener;
     let updateListener = (tabId, changeInfo, tab) =>
     {
@@ skipping 152 matching lines @@
         args: [
           {
             host: currentPage.url.hostname.replace(/^www\./, ""),
             whitelisted: !!checkWhitelisted(currentPage)
           }
         ]
       });
     });
   });
 });