To fix this, go into Firefox’s hidden configuration page by typing into the address bar “about:config”.
A warning will come up. Just click “I’ll be careful, I promise”.
Then filter the items you’re shown by typing “keyword”.
Double click on the Value for Keyword.URL and replace the value with the following (without quotes) “http://www.google.com/search?q=”
Try doing a keyword tag address bar search in Firefox: “g peanut butter”. Hopefully you’ll get something like this:
You may have to quit and restart Firefox to have this change take effect.