Issue 5965 - Handle edge case when searching for options page tab

lib/options.js

Index: lib/options.js
diff --git a/lib/options.js b/lib/options.js
index fa39d78374b04df576ddc85aedd5aea613fffe39..84adf19cc27921e40322c25e45135b3acadb3c66 100644
--- a/lib/options.js
+++ b/lib/options.js
@@ -38,7 +38,52 @@ function findOptionsTab(callback)
     // 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);
-    callback(tabs.find(element => element.url == fullOptionsUrl));
+    let optionsTab = tabs.find(tab => tab.url == fullOptionsUrl);
+
+    if (optionsTab)
+      callback(optionsTab);
+    else
+    {
+      // It seems that the url property isn't always set for the tab with
+      // Firefox 57 on Windows 10 until the tab has finished loading. Until
+      // then the url is given as "about:blank", but the title is the URL
+      // we expect (minus the protocol part).
+      let {hostname, pathname} = new URL(fullOptionsUrl);
+      let potentialOptionsTab = tabs.find(
+        tab => tab.url == "about:blank" &&
+               tab.title == hostname + pathname &&
+               tab.status == "loading"
+      );
+
+      if (potentialOptionsTab)
+      {
+        let onRemoved;
+        let updateListener = (tabId, changeInfo, tab) =>
+        {
+          if (tabId == potentialOptionsTab.id &&
+              changeInfo.status == "complete")
+          {
+            browser.tabs.onUpdated.removeListener(updateListener);
+            browser.tabs.onRemoved.removeListener(onRemoved);
+            if (tab.url == fullOptionsUrl)
+              callback(tab);
+          }
+        };
+        browser.tabs.onUpdated.addListener(updateListener);
+        onRemoved = removedTabId =>
+        {
+          if (removedTabId == potentialOptionsTab.id)
+          {
+            browser.tabs.onUpdated.removeListener(updateListener);
+            browser.tabs.onRemoved.removeListener(onRemoved);
+            callback();
+          }
+        };
+        browser.tabs.onRemoved.addListener(onRemoved);
+      }
+      else
+        callback();
+    }
   });
 }