One of the best! Rated 4 out of 5 stars

This is one of THE BEST extensions for the best browser around. I highly recommend it to all my FF using friends. You can configure it to use with just about anything that has a search text box. Here's what I currently have:

Google:
http://www.google.com/search?as_q=&hl=en&num=20&btnG=Google+Search&as_epq=$&as_oq=&as_eq=&lr=lang_en&cr=&as_ft=i&as_filetype=&as_qdr=all&as_nlo=&as_nhi=&as_occt=any&as_dt=i&as_sitesearch=&as_rights=&safe=off

Amazon:
http://www.amazon.com/s/ref=nb_ss_gw?url=search-alias%3Daps&field-keywords=$&x=0&y=0

Google Newsgroups:
http://groups.google.com/groups?hl=en&lr=&client=firefox-a&rls=org.mozilla:en-US:official&hs=FD1&as_qdr=all&q=%20%22$%22&btnG=Search&ie=UTF-8&oe=UTF-8&sa=N&tab=wg

Dictionary:
http://dictionary.reference.com/browse/$

and sometimes I'll swap Wikipedia for Dictionary:
http://en.wikipedia.org/wiki/$

The ONLY reason I didn't give this extension five stars is because you cannot determine how many options/"dictionary" searches you'd like to have. IOW, instead of having just 4 searches I'd like to have 5 or 6. I haven't dabbled in writing extensions for FF so I don't know how to edit the source code to do this. It would definitely be a nice feature the author could have have for the end users though. All in all, a great FF extension!

This review is for a previous version of the add-on (3.0.0).