Editing or adding a custom context menu item in Firefox?

Question

In Firefox when I highlight a text or phrase and right-click it, I noticed there's a sweet menu item called "Search Google for [highlighted text]". Now that I discovered it, I use it all the time for quick Google look-ups on things. But most of the time, I like to use it to look up a definition of a word I don't know.
My question is, how can I edit that menu item (or create a new one) so when I click that menu item, it pre-fills the Google search box with "define: [highlighted text]"? And if not, how can I create a context menu-item so I can look up words on a particular dictionary site?

Thanks for any insight!

Answer 1

The particular menu item you are referring to is tied directly to your selected search provider in the search bar in the upper right hand corner of Firefox. If you change your search provider to "Wikipedia" for example, you will now see "Search Wikipedia for [highlighted text]". You can find lots of new search providers on FireFox's Add-on site.

If you do want to add additional custom context menus, you will want to look into developing Firefox extensions.