I posted something previously on blocking social ads in facebook with greasemonkey, where I came to the conclusion incorrectly it could not be done with css. I apparently remembered what “! important” did in userContent.css and userChrome.css; I read “! important” as “not important,” but it aparently means the opposite, and overrides any webpages css. I corrected my post on userContent.css and userChrome.css customization as well. Stupid logic. Anyway, if you add the following block into your userContent.css file, you should be able to block most annoying stuff on both the new facebook design and old.

@-moz-document url-prefix(http://www.new.facebook.com/) {
.sponsor, .invitefriends, .findfriends, .gifts_received, .pymk, .social_ad, .adcolumn{
display: none ! important;
}
}

@-moz-document url-prefix(http://www.facebook.com/) {
.sponsor, .invitefriends, .findfriends, .gifts_received, .pymk, .social_ad, .adcolumn{
display: none ! important;
}
}

There may be a way to combine these two, but I don’t know the more mozilla-internal css well enough to know. If you use facebook, most of these should be clear. I blocked gifts, as I find them annoying, and I am glad to just not be aware of them. I also blocked the person finding features like “people you may know” (’.pmyk’) or the email search things. I also blocked ads of course. Facebook seems to have to idea that everyone will love ads if they are more specifically targeted at you, based on data they have on file. I can’t stop them from doing that (other than by closing and deleting my account), but I shouldn’t have to see ads if I don’t want to IMHO. Also notice that the new facebook design and the old one use the same css classes for everything; the redesign isn’t that extensive apparently.