Limited compatibility with Firefox 10 - some functions work Rated 3 out of 5 stars
Brilliant extension concept, but as others have said, it's unmaintained and badly broken. Options are broken, popup menu is broken, most functions are broken. It probably wouldn't need much work to get it compatible with Firefox 10.
But you can set options and colors etc via the prefs.js or about:config, and two core functions still work - Ctrl-Alt-(0 to 9) lets you color a tab or a domain as you want and the color is remembered properly. It also works well with Tab Mix Plus.
It's not much but that's all I wanted an extension to do, so although everything else is broken, FlagTab works for me. Can't wait for someone to bring it up to date for Firefox 10 though :)