The change between Firefox 3.6.* and Firefox 4 is how location bar search works. In Firefox 3.6 it uses Google "Browse by name" search. With the browse by name search, it performs a Google search and if there is a clear match it will take you to the site, otherwise it shows the Google search result. With Firefox 4 it just performs a Google search if you type something which is not recognised as a URL.

To get the Firefox 3.6 behaviour on Firefox 4 you need to change a hidden preference.

1. Type about:config into the location bar and press enter
2. Accept the warning message that appears, you will be taken to a list of preferences
3. Locate the preference keyword.URL, double-click on it and change its value to the link shown below

http://www.google.com/search?ie=UTF-8&oe=UTF-8&sourceid=navclient&gfns=1&q=

Thank you very much!!!!!

Tony E: I tried it a few days ago and it seemed to work. Not any more. The string you recommended, beginning "http://www.google.com/search?....." is still in the preferences at keyword.URL where you said to paste them. No other changes since first tried. Any ideas? Thanks/A

First make sure that the preference keyword.enabled is set to true.

Another possibility is you may have an add-on that is interfering with this. For details of how to troubleshoot that see https://support.mozilla.com/kb/Troubleshooting+extensions+and+themes