Rated 5 out of 5 stars
As a workaround if one of your add-ons won't install,instruct Firefox to stop checking the compatibility of all your add-ons. After you do this all your incomparable extensions Should automatically work. Note: On some you MAY notice they are not working exactly the same. Most will.
Naturally, doing so could put your system at risk but if you’re desperate to make an add-on work (like me), try this change at your own risk. 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.
Now Restart Fx
Hope this helps more then a few