Rated 5 out of 5 stars
I found a way to use this on FireFox 4! In your browser bar at the top type: about:config Click the "I'll be careful, I promise!" button if it pops up. Now right-click anywhere and click New>boolean. Name it: extensions.checkCompatibility.4.0 Then set it to false. Now close out of FireFox and open it back up and come back here. Click the "Add to FireFox" button and click "Install Anyway". When the box pops up click "Allow" and install it. Now restart your FireFox again and BAM there you go!