Add-On Compatibility Reporter for Firefox
Lifehacker reports on Add-On Compatibility Reporter which Enables Incompatible Firefox Extensions, Reports If Still Not Working.
The drawback to all the great addons available for Firefox (or any program that allows people to contribute like that!) is that each new version can disable, even temporarily, your favorite addon(s).
Addons have listings that say they have been tested with Firefox version this to version that. If you get a newer version, they are automatically disabled until updated.
Add-On Compatibility Reporter will re-enable them and let you test them. Then you can report that they still do or now do not work.