With apologies for being pedantic, but the proper term for Adblock Plus and so forth is "extensions." Firefox also supports "plugins" which are for things like PDF viewing, Flash, etc. I just now realized that you guys are talking about extensions but saying plugins.

The distinction is important, because, unless I'm mistaken, Chrome *does* support plugins, at least for Flash and various media players. It doesn't yet have the kind of extensions Firefox has, though, and it's not clear to me it has a mechanism for them like Firefox has with XUL.