Microsoft Windows XP

 

C:\Documents and Settings\{user}\Application Data\Mozilla\Firefox\Profiles\{profile folder}\
C:\Documents and Settings\{user}\Local Settings\Application Data\Mozilla\Firefox\Profiles\{profile folder}\Cache\

Microsoft Windows Vista / 7 / 8

 

C:\Users\{user}\AppData\Roaming\Mozilla\Firefox\Profiles\{profile folder}\
C:\Users\{user}\AppData\Local\Mozilla\Firefox\Profiles\{profile folder}\Cache\

Apple Macintosh OS X

 

/Users/{user}/Library/Application Support/Firefox/Profiles/{profile folder}/
/Users/{user}/Library/Caches/Firefox/Profiles/{profile folder}/Cache/

GNU / Linux

 

/home/{user}/.mozilla/firefox/{profile folder}/
/home/{user}/.mozilla/firefox/{profile folder}/Cache/