How do I stop this popup window: Error: 'navigator' getter called on an object that does not implement interface Window.
When I start Firefox a popup window appears: Error: 'navigator' getter called on an object that does not implement interface Window. My browser was left open overnight by mistake. I believe it may have updated.
Opaite Mbohovái (1)
Hello Mark Gilmour, try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes).
If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:
- click the menu button
, click Help 
and select Restart with Add-ons Disabled.
If Firefox is not running, you can start Firefox in Safe Mode by holding the Shift key when you open the Firefox desktop or Start menu shortcut. When the Firefox Safe Mode window appears, select "Start in Safe Mode".
If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.
To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.
Also you can create a new firefox profile, and see f the issue exist.
https://support.mozilla.org/kb/recovering-important-data-from-an-old-profile
thank you