Zach Tong has written a couple of great search tools for GMail. His GMail search plug-in for Mozilla integrates into the search bar (via the dropdown on the box) and invokes a GMail powered search using the terms you specify in the search box. This is a great little extension for Mozilla. I leave the search box set to GMail searches and use the Google toolbar for Google searches. Very handy.

Browser: Mozilla, Firefox, Netscape 7.x
Source: GMail Search Plugin