Rated 5 out of 5 stars
I have been using this addon for a while, especially since none of the competition work properly on Firefox4, and have been very pleased with it. However, now that I have discovered the autohide, hold control key to show option I am blown away.
Holding control (I set it to a shorter time delay) shows the tabbar (which is better vertically) in a gorgeous semi-transparent state, which overlaps the web page rather than squeezing it to the size. This gives an incredible combination of aesthetic and functionality.