Comment 15 for bug 850229

This should do it:

chr1s@farnsworth:~/src/messagingmenu-extension/messagingmenu-extension$ bzr commit -m "Instead of clearing the indicator when messages are removed from a folder, or when messages are read,
> just listen for the \"NewMessages\" boolean property on the folder changing to false. This should catch all cases and is aligned with
> how the \"new message star\" in the folder pane works" --fixes lp:850229
Committing to: /home/chr1s/src/messagingmenu-extension/messagingmenu-extension/
modified modules/MessagingMenu.jsm
Committed revision 90.
chr1s@farnsworth:~/src/messagingmenu-extension/messagingmenu-extension$ bzr push
Using saved push location: bzr+ssh://bazaar.launchpad.net/%2Bbranch/messagingmenu-extension/
Pushed up to revision 90.