I've been messing with user stylesheets the last couple of days, almost getting what I want, but not quite.
I'm a happy little firefox user, but the stock firefox functionality in this area really isn't that useful. My gripes:
first, firefox/mozilla seems to only support a single global user stylesheet, which gets huge and unwieldy awfully fast. Opera does this much better than firefox, I hear.
because of this, to apply styles to a particular site you have to use a magic
@-moz-document domainstyle modifier, and this doesn't seem to play nicely with
@mediamodifiers, so afaict there doesn't seem to be a way of specifying print styles for a particular site, say. If I'm wrong about this, I'd be happy to hear about it.
user stylesheets are local files, which means they don't follow me around across the different machines I use, and I don't get any network effects from the work of others, as is available using a 'cloud' solution like greasemonkey
(more minor) I know it's to spec, but having to specify
!importanteverywhere to force user styles to stick gets old fast
My other quibbles remain, though. In particular, there doesn't seem to be a nice way of setting up media-specific per-site styles, which is a must-have, I think. I'd also really love a solution that would follow me across browsers, especially given the number of sites you might want to tweak is typically much larger than the number of extensions you typically have installed.