I've looked at various suggestions to fix the above-reference problem and have checked that "open previous tabs and windows" is checked and that "clear history when Firefox closes" is *not* checked. But nothing is working. This started happening only a week or so ago. Thank you for ideas.

I also read that some add-in (?) or app (?) might be interfering. I can't remember adding anything new, but I wouldn't know how to check that.

Help/Troubleshoot Mode (FF Safe Mode) eliminates Addons influence. I keep a Spare "TEST Profile" to test issues with. See what the use of either / both do to your issue.

firefox.exe -p Put in RUN box and Profile Mgr results / Create New Profile and name it Test, etc. With 2 Profiles don't forget to chk the Box for your Default Profile "Use selected profile at startup without asking".

Desktop shtcut to open Test profile with default Profile Open "C:\Program Files\Mozilla Firefox\firefox.exe" -P TEST -no-remote

Desktop shtcut to open Test profile with default Profile Closed "C:\Program Files\Mozilla Firefox\firefox.exe" -P TEST

Thank you, CraigS26!

The part about the test profile went over my head and what followed went over my head. But the information about the troubleshooting mode turned out to be all I needed. I easily found out how to run it, and once I did, the problem was solved. (Simple, to-the-point instructions that work is one of the reasons I like Firefox.) I was even able to add back a "theme," possibly the same one, to get the comfortable colors I like seeing, and everything is working fine.

Thanks again.