One of the first I add after installing Firefox Rated 5 out of 5 stars
Great add-on, I've been using it for a long time. Especially docking "Downloads" is great (I hated Downloads window as separate window).
There used to some compatibility issues in the past, but now it works great (0.7.14 with Fx 7.0.1 + Greasemonkey, Stylish). If you use 3.6.* still, I recommend 0.7.11 version from here: https://addons.mozilla.org/pl/firefox/addon/all-in-one-sidebar/versions/ [however, it is incompatible with Greasemonkey].
@Conceit: I can resize to whatever width I want (but I upgraded from 3.6 to 7.0, not sure if this affects the case).