It kind of works, most of the time. On other occasions you'll get meeting reminders you can't dismiss, event cancellations which stack a new crossed out date on the list for every "update" click, events where you can't set attendance, and the annoying "you clicked dismiss, would you like to submit the modified event to the server" dialog. And that's on a good day :-(

There's lots of outstanding bugs unfortunately.

See https://bugzilla.mozilla.org/show_bug.cgi?id=1314185 - earliest dependent bug is 8 years old.