Great, but not without a bug! Rated 4 out of 5 stars
As a long time Firefox user, I've had this add-on installed since I was using Firefox 2, and it's probably the main reason I haven't switched to Chrome or any other browser, despite their innovations. I simply cannot image browsing without being able to quickly associate color with my websites. It's one of the greatest yet simplest innovations Firefox has ever had, and it's a shame the rest of the browser market hasn't caught onto this delicate nuance.
That being said, there has been a bug that's been bothering me for several versions now. Ever since Firefox 3.5, there has been an option to have "tabs on bottom." In this option, (at least on the OSX version; I'm not sure if I can speak for my fellow Linux or Windows users) the currently selected tab is always a few pixels larger than the other tabs. (unlike in "tabs on top," where all tabs are always the same size) However, in colorful tabs, every tab's color occupies a pre-defined amount of space, which means that, when a tab is selected and grows in size, there are a few pixels on the edge that are not shaded in. While this has not been annoying enough to make me stop using the add-on, it is a visual nuisance from time to time that makes the add-on, at times, feel cheap. I have posted about this problem several times through other media, but this has thus far proved unsuccessful. I love ColorfulTabs and would love to see it progress as an add-on, but currently there is a bug that has now existed for over a year! If it were fixed, I would truly consider ColorfulTabs the "perfect" add-on.
Thanks for reading.