1. In your Firefox address bar, type "about:config"
2. Yellow warning triangle will show up on the web page, but don't be alarmed, just click on "I'll be careful, I promise" button
3. In the FILTER bar, (looks like your typical address bar), type in "keyword.URL"
4. Double click it and another smaller window will pop up. Replace the highlighted text with the FOLLOWING text:
Note: If you can't see the entire text, just right click it and choose "Copy Link Location" and then PASTE IT in the box that I mentioned above.
5. Click OK and you have your Google back as your default search engine in your Firefox browser.