The latest Firefox beta is rather awesome, with tabs on top and a new menu that looks like an awful lot like Opera. It's very slick, until you try installing extensions that haven't updated yet. Here's how to force them to work.
Here's the error message we're talking about:
Side note: want to test the new beta out for yourself? Head over to the Firefox beta site.
Open up the about:config page, and then right-click anywhere and choose New –> Boolean.
You'll get a popup menu, at which point you'll want to use one of the two values as the preference name, depending on the version you're using:
4.0 Beta: extensions.checkCompatibility.4.0b
4.0 Release: extensions.checkCompatibility.4.0
Then set the value to false.
At this point your extensions should install just fine…
Important Note: At the moment of the writing of this article, Greasemonkey is really actually incompatible with Firefox 4.0 beta, and continually opens up the homepage with a never-ending list of tabs. The same goes for quite a few extensions that we tested, though some of them worked fine. We're pretty sure they'll be updated very soon.