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..88feed8d9d19e5177a18460ce62c4ca7cc97574e 100644
--- a/lib/options.js
+++ b/lib/options.js
@@ -38,7 +38,53 @@ 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);
+      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.
+    let potentialOptionTabIds = new Set(
+      tabs.filter(tab => tab.url == "about:blank" && tab.status == "loading")
+          .map(tab => tab.id)
+    );
+    if (potentialOptionTabIds.size == 0)
+    {
+      callback();
+      return;
+    }
+    let removeListener;
+    let updateListener = (tabId, changeInfo, tab) =>
+    {
+      if (potentialOptionTabIds.has(tabId) &&
+          changeInfo.status == "complete")
+      {
+        potentialOptionTabIds.delete(tabId);
+        let urlMatch = tab.url == fullOptionsUrl;
+        if (urlMatch || potentialOptionTabIds.size == 0)
+        {
+          browser.tabs.onUpdated.removeListener(updateListener);
+          browser.tabs.onRemoved.removeListener(removeListener);
+          callback(urlMatch ? tab : undefined);
+        }
+      }
+    };
+    browser.tabs.onUpdated.addListener(updateListener);
+    removeListener = removedTabId =>
+    {
+      potentialOptionTabIds.delete(removedTabId);
+      if (potentialOptionTabIds.size == 0)
+      {
+        browser.tabs.onUpdated.removeListener(updateListener);
+        browser.tabs.onRemoved.removeListener(removeListener);
+        callback();
+      }
+    };
+    browser.tabs.onRemoved.addListener(removeListener);
   });
 }