Rated 4 out of 5 stars

Has worked fine for me so far; works as specified in Firefox 3. One thing which would be even nicer would be if, rather than just creating solid icons, the extension created checkerboard patterns; basically, there aren't enough solid colors to make lots of tabs unique, but if you added a bit of a pattern, you'd have more options.

This review is for a previous version of the add-on (0.4.17). 

I am not totally convinced that this would work very well; However version 0.4.18 will allow a few more (currently 4) shapes to be set which may help a bit.

0.4.18f is currently under testing and is available from http://seis.bris.ac.uk/~ccjpb/