All firefox passwords are stored in three files
signons.txt, signons2.txt, key3.db
These files are stored in your firefox profile folder.
In Windows XP firefox profile is at:
c:Documents and SettingsWindowsUsernameApplication DataMozillaFirefoxProfilesprofilename
Copy these three files and save them where ever you want and if you want these passwords in your other os also then just replace these three files.
BAS
ENJOY