Download google toolbar for Firefox here
Some of Google's toolbar features people use it for are:
-highlight and find words on page
-all the same searching abilities you get by going to Google's own website
With Google now supporting both IE and Firefox, we have to wonder if Google's toolbar rival, MSN's toolbar, will also release Firefox support lol.
MSN's toolbar only supports IE, doesn't have the spell check, but has tabbed browsing and a search your computer for files option.