Rated 1 out of 5 stars

Can only search ONE engine at a time. the SearchWith add-on allows you to search MULTIPLE engines, each opening in it's own tab.
So ....it's kinda lame, cos it's not configurable.
Only adjustment is when you change the built-in Firefox searchbar
LAME!

This review is for a previous version of the add-on (3.18). 

SmartSearch includes a "Search All in Tabs" item in each folder, which you can use to perform multiple searches at once.

I notice from another review that you wish that SmartSearch could open text URLs. For some reason, Firefox doesn't allow us to create a quicksearch with URL "%S," which would solve the problem, but as a workaround, you can use "http://hiderefer.com/?%S" instead.

I admit that SearchWith, Context Search, and SmartSearch differ primarily in where their searches come from. If you don't want to your extension to take searches from bookmarks, then SmartSearch isn't going to be the best choice for you.