I'm not sure I understand how your toolbars are set up. The main navigation toolbar usually has a URL bar (address bar) which you can use to search (in Google by default), and a separate search bar/search box with a drop-down to choose a search engine. Do you have a different setup?

Could you reply with a screen shot (you can attach images using the Browse... button below the text compose box)? This article might help: How do I create a screenshot of my problem?

See:

• http://kb.mozillazine.org/Unable_to_search_or_add_new_engines

Try to reset some preferences to the default with the SearchReset extension:

• https://addons.mozilla.org/firefox/addon/searchreset/

Note that the SearchReset extension only runs once and then uninstalls automatically, so it won't show on the "Firefox > Add-ons" page (about:addons).