hello, can you try to replicate this behaviour when you launch firefox in safe mode once? Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

could you please also go to the firefox menu ≡ > help ? > troubleshooting information, copy the contents of that page and paste them here into a reply on the forum? this might give us a clue what is going on...

Some have reported that pressing F9 and the Windows key simultaneously one or more times has worked to fix issues with the keyboard not working. If this doesn't help then close and restart Firefox or reboot the computer (you may have to reboot more than once).