Site-specific browser extensions

Adrian Holovaty, frustrated with a backward redesign of All Music Guide, has written an extension for Mozilla Firefox that modifies the site behavior to his liking. He calls for more:

There's a huge potential here. Site-specific Firefox extensions are an elegant, one-click-install solution to the problem of, well, lousy Web interfaces -- a problem Web users have had to shut up and deal with for as long as the Web has been around.

Along the same lines, the BugMeNot extension embeds the functionality of BugMeNot right within a Mozilla/Firefox/Netscape browser.

I like the idea a lot, using the potential of the web as a platform and routing around monoculture, annoyances and mediocrity.