The AppData folder is a hidden folder; to show hidden folders, open a Windows Explorer window and choose "Organize → Folder and Search Options → Folder Options → View (tab) → Show hidden files and folders".
On Windows 2000, XP, Vista, and Windows 7, you can also use this path to find the profile folder, even when it is hidden:
%APPDATA% is a variable represents the C:\Documents and Settings\<user name>Application Data folder on Windows 2000/XP and the C:\Users\<user name>\AppData\Roaming folder on Windows vista and Windows 7.
To find a profile folder in the default location on Windows 2000, XP, Vista, or Windows 7:
Press "Windows key Image:Windows_Key.png + R" to open the Run box
(or, you can click "Start → Run..." on Windows 2000/XP)
In the Run box, type in %APPDATA%
Click OK. A Windows Explorer window will appear.
In this window, choose Mozilla → Firefox → Profiles.
Each folder in the "Profiles" folder (e.g., "xxxxxxxx.default") is a profile on your computer.