xpi install of plugin to user specific area on unix

I have an xpi script to install a mozilla plugin. It uses getFolder to
find the directory where it can install but there is no option to get the
home
plugins/components directory.
I could do something like getFolder("Current User",../../plugins) but
this is horrible though works for at least the default environment.
I really need to get to ~/.mozilla/plugins & ~/.mozilla/components since
most users wont have write permission in the main install of mozilla which
is what is returned by getFolder("Plugins").


Thanks

John