Removing The 'Go' Button Firefox 2 Only
Removes the ‘Go” button from the address bar

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Tweak Type:	Display
Fx 2:	YES
Fx 3:	NO
Fx 3.1:	NO

Note: Current versions of Firefox 3 and Firefox 3 have removed the 'Go Button' by default

With the new default theme for Firefox 2 there is not a ’simple’ way to remove the ‘Go’ Button from the navigation toolbar. I never used the go button since I simply press enter after I type in address. This will make your address box a little bigger as well. There a couple ways you can remove the Go Button either via about:config or modifying your userChrome.css file.

about:config method

1. Open a new tab and type about:config in the address bar OR if you are using the about:config extension, click the about:config button
2. In the filter box type (or paste) browser.urlbar.hideGoButton
3. The default settings is FALSE – double click anywhere on the entry to change it to TRUE
4. Changes are effective immediately

userChrome.css file method - 
Note: to use this method you need the ChromEdit Plus extension

1. From Firefox tools menu select ChromEdit Plus and then select ChromEdit from the sub menu
2. ChromEdit will open in a new window (or tab). Go to the bottom of the document and paste:
   #go-button-stack, .search-go-button-stack {
   display: none !important;
   }
3. Click the ‘Restart Firefox’ button in ChromEdit
4. Changes are effective after Firefox restarts

Source