Fix Firefox web_accessible_resources: use extension_ids instead of moz-extension matches

Firefox's match pattern validator does not allow the moz-extension:// scheme
in matches. Use extension_ids: ["*"] so extension pages can load the
resources without invalid manifest error.

extension/manifest_firefox.json

@@ -74,9 +74,7 @@
         "dashboard/events.js",
         "background/*.js"
       ],
-      "matches": [
-        "moz-extension://*/*"
-      ]
+      "extension_ids": ["*"]
     }
   ],
   "icons": {