Rated 5 out of 5 stars

Windows 9x/Me C:\WINDOWS\Application Data\Mozilla\Firefox\Profiles\xxxxxxxx.default\
Windows2000/XP/2003 C:\Documents and Settings\[User Name]\Application Data\Mozilla\Firefox\Profiles\xxxxxxxx.default\
Windows Vista/7 C:\Users\[user name]\AppData\Roaming\Mozilla\Firefox\Profiles\xxxxxxxx.default\
Linux ~/.mozilla/firefox/xxxxxxxx.default/
Mac OS X ~/Library/Application Support/Firefox/Profiles/xxxxxxxx.default/

extensions\{d650973c-0444-4ac7-9d00-19e3613c83b9}\install.rdf

<em:maxVersion>3.6.*</em:maxVersion>