Rated 5 out of 5 stars
Very cool. I do have one suggestion though. If you could please change line 260 of extensions_override.css, (for .category) from "width: 4.5em;" to "min-width: 4.5em"? Hard-coding the width like this makes it inflexible to some modifications I'm doing. It would also be nice if your extension added an attribute or a class to #addons-page so that userstyles, themes, and extensions could actually support it. It's impossible to detect if it's on from CSS.
Edit: Thanks... I figured out a way around it: width:100%!important; ... this overrides the fixed width and uses the appropriate width for the content. Trying to get everything to work in my latest version of SeaFox, which has even more "classic" look. :)
An attribute makes a lot of sense; I'll add that.
I looked at the "width: 4.5em" rule... and it looks like it's completely unnecessary. It renders exactly the same without it, even back in Firefox 5.0. Which means I need to work out why it was there in the first place...
(I also need to work out how to handle the CtP plugin setting UI, which has been semi-broken for far too long, so it's going to take me a few days to upload a new version, plus however long it takes to get reviewed after that.)