This was just running through my mind: What is the most annoying thing (or was) with Mozilla Firefox updates? Extensions that told you they weren’t compatible. But actually there haven’t been huge changes between minor versions, just bug fixes. Still these extensions weren’t meant to function. Firefox won’t let you. I think this is a mistake.
If a user wants something, he should always be able to do it. If he wants to run extensions that aren’t meant for the most recent version, he should still be able to run them nonetheless. Display a warning, ask for permission, but never block anything so much, that you can’t use it unless you crawl deeply into configuration files or menus.