Rated 3 out of 5 stars

This extension will work with 3.5.x as long as you use Mr Tech Toolkit to allow for it, or modify the install.rdf file. I take away 1 star because the domain name for the project is gone. And another for not being directly 3.5 compatible. Still it does work.

On another note the extension I now use to replace this is CuteButtons Crystal SVG which is 3.5 compatible from the start. Others might find Menu Icons Plus more to your liking especially if you like tweaking Firefox rather than just having something work. So there are plenty of options for those not wanting to take the time to make this extension compatible...