Try to rename/remove xulstore.json in the Firefox profile folder with Firefox closed.

You can use the button on the "Help -> More Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page (Root directory).

• Help -> More Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

Well it turns out it's not Firefox in particular. I found that the Settings and Thunderbird Email apps also expand beyond the display area when the laptop is put in standby mode and then is turned back on. Thus it makes sense that none of the Firefox specific solutions solve the problem. This problem began around the last time I updated Ubuntu. Hmmm... In all cases the problem is solved by hitting the maximize button twice.

I've run into this issue on Ubuntu as well, for all manner of programs. I can't say whether it is the same exact thing or not, but it sounds very similar. My solution? Workarounds.

It seemed like minimizing the window before closing the lid, caused it to restore to the proper size once I wake the system. Also, it seemed like not closing the lid, but instead giving the sleep command, seemed to prevent this. And yes, toggling the maximize button also worked for me. I was blaming the hardware, assuming that the laptop was changing screen resolution for the video output port (due to the internal screen being disabled), or something like that. However, it could be something else entirely.

Thanks to Figure8565 for the confirmation. I'll mark this problem as solved since it is not a FireFox specific problem. Willie