Firefox: Maybe you've seen your favourite extensions fall behind when new Firefox releases roll out, but you haven't known what to do about it. A new-ish Mozilla add-on not only enables technically incompatible extensions for testing, but makes reporting actual incompatibilities easy.
Some of your favourite extensions might have authors that view them mainly as side projects, and can't always test and release new versions with every Firefox alpha, beta and final release. Some of their extensions, though, may work just fine with a newer Firefox, but they just haven't updated their code to affirm that. Mozilla's Add-On Compatibility Reporter lets you, the extension fan, enable and test out extensions on any version of Firefox, then report if they're working fine or need some work.
It's a smart thing for Mozilla to make it easier for non-programmers to help with testing and reporting of extension compatibility. Your reports go to Mozilla, not the extension author, so you don't have to worry about embarrassing yourself in front of those clever types (trust me, it's a real concern). And for users who feel like they're lost at sea without their favourite Firefox tweaker, there's a way to verify that it really works, or actually doesn't, without having to hack your browser to make extensions compatible.
Add-On Compatibility Reporter is a free download, and technically works with Firefox versions through 3.7 alpha 1—though I couldn't install it from Mozilla's site while using the 3.7 alpha 1. Tell us if this extension has helped you test and report your own oft-neglected favourites in the comments.
Add-on Compatibility Reporter [Add-ons for Firefox]