http://www.mozilla.com/en-US/firefox/system-requirements.html
Firefox 2 System Requirements
Windows
Minimum System Requirements
* 233 Mhz processor
* 64 MB of RAM
* 50 MB of free disk space
* Microsoft Windows 98
Mozilla Recommends
* 500 Mhz processor
* 256 MB of RAM
* 100 MB of free disk space
* Microsoft Windows XP
Uzgred, ovo je forum "UNIX Desktop/X Window System", mozda tvoje pitanje nije za ovde, jer X Window System nije Windows OS, ali nije bitno.
Na svetu postoje samo 2 OS-a: 1. Mint, 2. svi ostali!