I assume exiting Firefox and starting it back up again hasn't helped. At the risk of sounding like a cliché, have you tried doing a regular shutdown and restart of Windows in case there is some transient glitch with how mouse input is communicated between Windows and Firefox?

Yes, tried all that several times, cleared my cache as well etc. . Am also having trouble with drop down boxes not recognizing mouse keys anymore, seemed to happen overnight. thanks though

Do you have a paired, wireless keyboard and mouse? If so, they may need new batteries.

No, they work just fine, I have the same problem if I use the laptop keyboard and touchapad mouse. It's a software problem that started after the most recent update.

I have an add-on whose preferences, among other things, includes "Ignore full zoom changes made by browser". Since I don't have your issue, I don't know whether that would solve it. On most sites (not this one) it allows you to change the font size as well as or instead of zoom. https://addons.mozilla.org/en-US/firefox/addon/zoom-page-we/ Another option is to try another profile: https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles

Also, does it happen in safe mode? https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode

yes. booting in safe mode makes no difference. It's not an add on or extension its the program