If you would like to add search engines to Firefox then click here.
Search engines
Also if you would like to remove a search engine then click on
My Computer,
C: drive,
Program Files,
Mozilla Firefox,
searchplugins,
delete what you don't want then restart Firefox.
I found it easier to remove them all then reinstall what I wanted.
You'll get a small input window with a google symbol in it on your task bar with a drop down arrow. I've installed Google UK and Google Images.