Hi Stuart,

We are referring to the ADD-ON google toolbar. All versions of FF have a Google (default) search box to the left of the address bar. (You can actually set it to be a search box for a number of different search engines by clicking on the down diamond next to the search logo)

If you are runng FF3 under Linux you will find on your tools menu where it says add-ons.
when u click on it it should open a seperate window with several choices. You want to click on the icon that says "Extensions."
This see more will list the extensions (add-ons) you have installed. Scroll down the list and look for Google Toolbar. When you find it click on it and then click on the "Disable" button.
You will be required to restart FF after you disable the extension.

If you are not showing the google toolbar installed the you are experiencing some other issue than the one discussed here.

Also, try starting your firefox in safe-mode
"firefox -safe-mode" Then try resetting things to the default and disable all add-ons/Extensions.

Once you have determined that this works then use tool->addon to re-enable your extensions 1 by 1.