How to make this work in 4.0 Rated 5 out of 5 stars
You can update this yourself to 4.0, albeit it looks off when you do. (I have to resize it, but it works the same.)
Go to where you can download the add-on and right click on the link. Save the file to your desktop.
Add to the extension ".zip" and open the file. Take out the file named install.rdf and open it with notepad.
Change the max version to 4.0.* or whatever. (4.6.* works too)
It's the line here:
Save it, put it back in the zip, remove the zip extension, and drag the file to an open browser window. Restart firefox.