hello, can you try to replicate this behaviour when you launch firefox in safe mode once? if not, maybe an addon is interfering here...

Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

Hello,

Are those tabs blank or do they contain ads? Also did you download Firefox from a Mozilla website?

• https://www.mozilla.org/en-US/firefox/new/

If you downloaded Firefox from a third party, you may have downloaded Firefox bundled with PUP (potentially unwanted programs), and it would be advised to remove Firefox along with suspicious programs in Control Panel > Programs and Features. In that scenario, download Firefox again from the link above.

You may want to run a scan with some anti-malware software:

• MalwareBytes' Anti-Malware
• AdwCleaner (for more info, see this alternate AdwCleaner download page)
• Further information can be found in the Troubleshoot Firefox issues caused by malware article.

I open Firefox in Safe Mode as you suggested. The problem did not reoccur, so I followed the directions to un-check hardware acceleration. That seems to have fixed the problem. Thank you.

I downloaded from Mozilla website. I regularly use Anti-Malware and other protective programs.