Hmm. Looks like a search engine issue. I'm guessing here - try left clicking the Google icon, and then go to "Manage Search Engines".
Remove all of them. Then restart Firefox and see if that fixes the problem. If it does, add each search engine you use one by one until you hit the problem again.
If you're lucky the ones you want to use aren't the ones causing the error, and you can just ignore the one that did.