Bug 1091299 - It's possible to open the SMS activity menu multiple times

too bad we don't have a real button like https://bugzilla.mozilla.org/show_bug.cgi?id=1014219 should do

maybe we can simulate a "disabled" attribute by using pointer-events: none?
and even, it's maybe a good idea to set pointer-events: none on the whole interface except the menu, right? Because I suspect the issue can happen in other places too.