Bug 1041303 - Directly launch SMS while user click in utility tray

r=alive

Direct launch SMS app while user click message in utility tray. And because SMS app will show thread list in the circumstances, we also disable pointer event for this moment.

https://bugzilla.mozilla.org/show_bug.cgi?id=1041303
nit: If you prefer to wrap the classList action into function, please sync the behavior here as well.