That old computer should be just fine with Firefox 4. In fact I run FF4 on an older Dell Dimension 8200 - P4 @1.7Ghz, 512MB RAM. (Secondary comp). And I run FF 3.6 on another Dell Dimension 8200 - P4 @2.2Ghz, 512MB RAM. (Primary computer).

Because I obviously live on Antartica, and have unlimited access with no caps. All the pr0n and free movies I want. Troll that, you homosexual noobs!