If there is no support for notifications, the only menu item at the moment, don't show the menu since the state of the checkbox is irrelevant to the user.
Tweaked line-height for the menu item's checkbox.
Close notifications after 10s for browsers that leave them up forever by default.
Seeking backwards from a stream that ended has a last value off the end of the chat array, so go back one to start from a valid entry in that case.