And now I notice that if I have an email open, and depress the Ctrl key the mail starts zooming out ad infinitum.

Is there some simple way to roll back an update to see if that's what's causing a problem? All I can see is to do a total uninstall, reinstall and hope that the various data files and links don't evaporate.

Installing TB 60.4.0 did not change the problems any... Rolling back Firefox to 62.0.3 didn't help either. Nor did rebooting the computer.

So now I tried rolling back my System Restore to Dec20. Windows says it cannot be done, the update failed for unspecified reasons. None-the-less the down level TB seems to be working properly again. I'm done. In theory I should allow TB to update now to complete the experiment but I've had enough of pointless screwing around with computers for the day. Time to actually get something accomplished.

And I see the same zooming problems on a different Win 10 machine on which I haven't actually run TB since I installed it months ago.

Though there seems to be no interest in this at all, let me state that I may have found the problem. It's apparently well known that the mouse software can go subtly haywire and act as if one is spinning the wheel to turn volume all the way down which I also experienced. Turns out this seems to also be my Thunderbird problem - it thinks the mouse wheel is spinning when one tries to access the printer selection box, so it always "spins" up to select the top printer - which in my case is the PDF output.

I've changed out the mouse and so far it seems to solve the Thunderbird problem. We'll see if this "solution" fails in a week or not. The mouse I swapped out was a Logitech, FWIW.