How To Bypass Firefox 4.0 Beta’s Incompatible Add-on Error and Install Extensions Anyway

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 all very slick, until you try and install your favorite 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, though it’s really in beta, and has a lot of changes, so you’ll want to think carefully before you do so.


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.

Lowell Heddings is the founder and Editor-in-Chief of How-To Geek. He spends all his free time making sure this site can bring you fresh geekery on a daily basis, and has been doing so for over eleven years.