Well, that's annoying.

On Mac, Command+Shift+f should switch the display between the regular view and full screen view. Does that work?

If you still can't access the menu bar, one of Firefox's settings file might have become corrupted. Try this, assuming you have the main toolbar:

Open your current Firefox settings (AKA Firefox profile) folder using either

• "3-bar" menu button > "?" button > Troubleshooting Information
• type or paste about:support in the address bar and press Enter/Return

In the first table on the page, click the "Show in Finder" button. This should launch a new window listing various files and folders.

Leaving that window open, switch back to Firefox and Exit:

• "3-bar" menu button > "power" button

Pause while Firefox finishes its cleanup, then rename xulstore.json to something like xulstore.old. If you see a file named localstore.rdf, rename that one to localstore.old.

Start Firefox back up again. Do windows display normally again?

Hitting Command+Shift+f worked as you hoped and from there I simply opened a new FireFox page & closed the error message page. I've tried quitting FireFox and rebooting FF and it appears be working. Any tips on how to avoid that happening again? Like if FF quits on its own (that may have happened before this problem occurred) or should I before shutting down follow a procedure in closing FF? Thank you so much!

It's best to use Quit to shut down Firefox instead of allowing the operating system to terminate Firefox. That helps ensure that any "clean up" tasks Firefox needs to perform in the settings folder are completed. Sure, things will still go wrong occasionally, but hopefully fewer things.

OK, upon shutting down the computer, I'll always first quit Firefox.

Thanks again, and

Best regards,

TerryRoss