87887 - don't call InitPolicies or InitPrincipals if there are no prefs to process
83902 - Use weak reference to pref branch to avoid reference cycle
91619 - was leaking a char* - use nsXPIDLCString instead
86932 - Add support for per-site JS disabling to CanExecuteScripts
all bugs r=jesse, sr=dougt
git-svn-id: svn://10.0.0.236/trunk@100226 18797224-902f-48f8-a5cc-f745e15eee43