Microsoft Windows XP
History, Downloads and Cookies
C:\Documents and Settings\{user}\Application Data\Mozilla\Firefox\Profiles\{profile folder}\
Cache
C:\Documents and Settings\{user}\Local Settings\Application Data\Mozilla\Firefox\Profiles\{profile folder}\Cache\
Microsoft Windows Vista / 7 / 8
History, Downloads and Cookies
C:\Users\{user}\AppData\Roaming\Mozilla\Firefox\Profiles\{profile folder}\
Cache
C:\Users\{user}\AppData\Local\Mozilla\Firefox\Profiles\{profile folder}\Cache\
Apple Macintosh OS X
History, Downloads and Cookies
/Users/{user}/Library/Application Support/Firefox/Profiles/{profile folder}/
Cache
/Users/{user}/Library/Caches/Firefox/Profiles/{profile folder}/Cache/
GNU / Linux
History and Downloads
/home/{user}/.mozilla/firefox/{profile folder}/
Cache
/home/{user}/.mozilla/firefox/{profile folder}/Cache/