Rated 5 out of 5 stars
This is #1 among my extensions. Simply by making bookmarks with %s as search term I create as many needed "extensions" as I need. Search Google, WhoIs, Backwards, Open link, see number of indexed pages, translate word - Everything with just one click! I combined it with Smart Bookmarks Bar and now have a lot of icons on my Bookmarks Toolbar that save space and actually are not bookmarks but real tools.
Please make it compatible with FireFox 3.0, because I can't upgrade just because of this must have extension