Issue 5347 - Check for windows API support

ext/background.js

Index: ext/background.js
===================================================================
--- a/ext/background.js
+++ b/ext/background.js
@@ -512,21 +512,24 @@
           updateContextMenu();
         }
       }
     }
   };
 
   chrome.tabs.onActivated.addListener(updateContextMenu);
 
-  chrome.windows.onFocusChanged.addListener(windowId =>
+  if ("windows" in chrome)
   {
-    if (windowId != chrome.windows.WINDOW_ID_NONE)
-      updateContextMenu();
-  });
+    chrome.windows.onFocusChanged.addListener(windowId =>
+    {
+      if (windowId != chrome.windows.WINDOW_ID_NONE)
+        updateContextMenu();
+    });
+  }
 
 
   /* Web requests */
 
   let framesOfTabs = new Map();
 
   ext.getFrame = (tabId, frameId) =>
   {
@@ -729,45 +732,59 @@
     else
     {
       // Edge does not yet support runtime.openOptionsPage (tested version 38)
       // nor does Firefox for Android,
       // and so this workaround needs to stay for now.
       // We are not using extension.getURL to get the absolute path here
       // because of the Edge issue:
       // https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/10276332/
-      chrome.windows.getLastFocused(win =>
+      let open = win =>
       {
         let optionsUrl = "options.html";
         let queryInfo = {url: optionsUrl};
 
         // extension pages can't be accessed in incognito windows. In order to
         // correctly mimic the way in which Chrome opens extension options,
         // we have to focus the options page in any other window.
-        if (!win.incognito)
+        if (win && !win.incognito)
           queryInfo.windowId = win.id;
 
         chrome.tabs.query(queryInfo, tabs =>
         {
           if (tabs && tabs.length > 0)
           {
             let tab = tabs[0];
 
-            chrome.windows.update(tab.windowId, {focused: true});
+            if ("windows" in chrome)
+              chrome.windows.update(tab.windowId, {focused: true});
+
             chrome.tabs.update(tab.id, {active: true});
 
             if (callback)
               callback(new Page(tab));
           }
           else
           {
             ext.pages.open(optionsUrl, callback);
           }
         });
-      });
+      };
+
+      if ("windows" in chrome)
+      {
+        chrome.windows.getLastFocused(open);
+      }
+      else
+      {
+        // Firefox for Android does not support the windows API. Since there is
+        // effectively only one window on the mobile browser, there's no need
+        // to bring it into focus.
+        open();
+      }
     }
   };
 
   /* Windows */
   ext.windows = {
     create(createData, callback)
     {
       chrome.windows.create(createData, createdWindow =>