This is a question we get time and time again, so I thought I would post the full listing for where your profile folder is for Mozilla Firefox based on your operating system of choice…

Windows 95 (without Desktop Update)
C:WindowsMozilla

Windows 95 (with Desktop Update)/98/Me
C:WindowsApplication DataMozilla

C:WindowsProfiles<Windows login/user name>Application DataMozilla

Windows NT 4.x
C:WinntProfiles<Windows login/user name>Application DataMozilla

Windows 2000 and XP
C:Documents and Settings<Windows login/user name>Application DataMozilla

Windows Vista
C:Users<Windows login/user name>AppDataRoamingMozilla

Unix
~/.mozilla/

Mac OS X
~/Library/Mozilla/

~/Library/Application Support/

This post from the Mozilla Knowledge Base should also help:

http://kb.mozillazine.org/Profile_folder_-_Firefox

Hope that helps you locate your Firefox profile folder.  If there is a location I missed, be sure to let me know and I will get it added.