Do the buttons work properly in safe mode (Help/Restart with Add-ons Disabled)? You might need to 'reset toolbars and controls'.

Just restarting Tbird fixes it. Then it may be a day or so until it happens. I will do a restart in safe mode and see if it happens again. I was hoping it was a known problem.

It's a known issue in that the update from 68 to 78 has been plagued with display and other issues. The best way to avoid them is to not run 78 on a profile previously run in 68 but to create a new profile with 78.

For me, rebuilding the profile is a big deal. I have 8 different email accounts and 21 years of Tbird emails in about 80 different folders. Last time I rebuilt my profile, it took me days to get rid of the duplicate emails and other problems. (POP3, not IMAP here, so a lot of data). A lot of the recent updates have been more problems due to all the 'new' stuff that I did not need breaking all the good 'old' stuff that I was really happy with. I think Mozilla, as a whole, has left their roots of providing better, faster, less bloat-ware products. Over the last 5-8 years, Mozilla seems to have gone down-hill due to "over-engineering" everything. It's sad. ;-(