Rated 5 out of 5 stars
Since my last link has been moved down quite a bit, I am re-posting it here:
You cannot use the version found here on any version of Firefox greater than 3.x. They made changes to the way extensions are handled in 4.x and again in 5.x. I have modified the addon to work with both versions and have it available for download here: My Release - Fixed for 4.x & 5.x
To install it:
1) Download the archive from the link above.
2) Remove the existing addon from Firefox and restart Firefox.
3) Click on File->Open and browse to where you downloaded it to.
4) Select the archive and let it install.
Now, If you don't trust my code that's fine. If you read through all of my reviews here I describe exactly what changes were made to get it to work. You can download the version here and make those changes manually to get it to work with FF 4.x & 5.x
I simply provide the modified archive for those who are not technically inclined.