I can't remember if it was right when I updated to v.22, but if not then it was shortly after that my mouse wheel stopped working for scrolling through tabs. I can still scroll through pages just fine, but even on safe mode and with hardware acceleration disabled, if I put my cursor over tabs and scroll, nothing happens.
note that to scroll through tabs with mouse wheel, you can position the mouse cursor, between the two arrows at each end, of the row of tabs. That means that you have quite a few tabs to see the arrows at each end.
otherwise, Try Firefox Safe Mode to see if the problem goes away. Safe Mode is a troubleshooting mode, which disables most add-ons.
(If you're not using it, switch to the Default theme.)
Once you get the pop-up, just select "'Start in Safe Mode"
If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, and you need to figure out which one. Please follow the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article for that.
To exit the Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.
When you figure out what's causing your issues, please let us know. It might help other users who have the same problem.
Note that you can double-click a scroll button to move the tabs one screen or triple-click a scroll button to go to the begin (first tab) or end (last tab).
Unfortunately I use many, many tabs and the mousewheel is (was) far and away the easiest method to navigate them.
Does no one have any idea why mouse wheel scrolling tabs wouldn't even work in safe mode?