DeeperWeb
Google must die!!! Google must die and be reborn not just "die" of course. Why? Just perform a few searches and you'll get your answer... or get DeeperWeb and take your Google user experience to a whole new level right here and right now! Since the choice is obvious let's take a closer look at it shall we? ;)
Compatible with Firefox 3.0 - 3.6.* and released quite a while ago back in mid-June 2010 DeeperWeb is surely a Firefox addon you don't want to miss - it's free has a rating of 4 stars after 39 reviews and 170104 downloads so far. Its Mozilla page can be found here while the official product page is this one. You'll find plenty of information there but...
... I am sure you weren't expecting this to end without me sharing the experience I had with DeeperWeb right? Well two things need to be said here - first I'll definitely keep DeeperWeb as my primary search engine on Firefox but unfortunately there's also still one simple setting I'd like to be able to mess with: the ability to completely take out of the picture the "classic" Google results. That next to other few things would really turn this little gold nugget into a ridiculously expensive pearl. I know this may not say too much about the user experience but it will only take a few minutes to get started with DeeperWeb so... what are you still waiting for Easter? ;)