If you miss to the triangular one (relevant for the windows users only. I'm not so sure about it, though).
Icon from:
http://mxr.mozilla.org/firefox2/source/browser/themes/winstripe/browser/Go-arrow.png
CSS code from:
http://mxr.mozilla.org/firefox/source/browser/themes/winstripe/browser/browser.css#1228
http://mxr.mozilla.org/firefox/source/browser/themes/pinstripe/browser/browser.css#1051
You might want to check these also/instead:
▷ Firefox 3 - Go button always visible by LouCypher
▷ Fx3 - Oldstyle Go Button by Sid
Before
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After
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.ad {
/* Your ad can be here instead. 10K unique visitors for $5/day. Mail me. */
}