Firefox Extension Guru's Tweaks

Removing The Search 'Go' Button
Removes the Magnifying Glass ('Go') button from the search box

Tweak Type:	Display
Fx 2:	YES
Fx 3:	YES
Fx 3.5:	YES

The userChrome.css file is located in the Chrome folder in your profile folder and can be edited with notepad. I would though recommend getting the ChromEdit Plus extension as this makes this process so much easier.

Firefox 2

To remove the search button (magnifying glass) add this line:

.search-go-button-stack { display: none !important; }

To remove the ‘Go’ Button on the navigation bar add this line:

#go-button-stack { display: none !important; }

If you also want to remove the search engine drop-down button as this line:

.searchbar-engine-button { display: none !important }

After you have made the change and saved your userChrome.css file, you will need to restart Firefox for the changes to take effect.

Firefox 3

To remove the search button (magnifying glass) add this line:

/*Remove
the search button (magnifying glass) */

.search-go-button { display: none !important; }

Sources: Firefox 2 | Firefox 3/3.5