Most people probably know the feature when you right click some text on a web site you can do a google search on it ( Search Web for...) . This feature has been enhanced by Cusser, a user on Mozillazine who already has created a few extensions you can see on his web site http://www.cusser.net/extensions/
The search extension will allow you to not only do searches in google, but also other web sites. Imagine you are a movie buff ( like me) Then you could right click the name of a movie in your tv listing and then search for it on IMDb in a new tab.
You simply go to the google search box, click on the google icon and add the search engines you want to have acces to. If you have installed the extension from Cusser you can right click on some text and make search for it in a dictionary, IMDb or another site you like. You are no longer restricted to google.
You can get the extension here http://extensions.cusser.net/contextsea
Great work, Cusser. This is a very good extension.