prefs: tests: port old xpcshell-based test to jstest
http://bugs.activestate.com/show_bug.cgi?id=101666

(integrated from komodo (trunk) change 83354 by marky)

git-svn-id: http://svn.openkomodo.com/repos/openkomodo/trunk@14088 b87d16e7-d29f-4ee1-b5ec-817d645d335f