--- a/browser/base/content/webrtcIndicator.js
+++ b/browser/base/content/webrtcIndicator.js
@@ -34,16 +34,20 @@ function init(event) {
   // Alert accessibility implementations stuff just changed. We only need to do
   // this initially, because changes after this will automatically fire alert
   // events if things change materially.
   let ev = new CustomEvent("AlertActive", {bubbles: true, cancelable: true});
   document.documentElement.dispatchEvent(ev);
 }
 
 function updateIndicatorState() {
+  // If gStringBundle isn't set, the window hasn't finished loading.
+  if (!gStringBundle)
+    return;
+
   updateWindowAttr("sharingvideo", webrtcUI.showCameraIndicator);
   updateWindowAttr("sharingaudio", webrtcUI.showMicrophoneIndicator);
   updateWindowAttr("sharingscreen", webrtcUI.showScreenSharingIndicator);
 
   // Camera and microphone button tooltip.
   let shareTypes = [];
   if (webrtcUI.showCameraIndicator)
     shareTypes.push("Camera");