Rated 5 out of 5 stars
As a workaround if one of your add-ons won't install, Tell Firefox to stop checking the compatibility of all your add-ons. After you do this all your compatible extensions Should automatically work. Note: On some you MAY notice they are not working exactly the same. Most will though.
Naturally, doing so could put your system at risk but if you’re desperate to make an add-on work (like me), try this. I do/did for Every ver bump & all is well so far. That, or you can edit every .rdf file but that's a pain right?!
Type "about:config" without the " " in the address bar & hit enter....
Then right-click anywhere in the about:config list of settings & choose New, Boolean. When prompted, type extensions.checkCompatibility, press Enter. At the second prompt, select false & press Enter again.
Restart Fx. Bam! Done!
Hope this helps
FYI: Any custom changes you or your extensions make will be in bold in about:config