From parent bug: I was under the impression that sessionstore-windows-restored is the notification used for this purpose, but as it turns out, that notification is only sent during the initial restoring of the windows and tabs the first time that the browser is starting up, and because many users (both in-tree and possibly extensions as well) rely on it to detect the browser startup, we need a new topic, which I'm going to tentatively name sessionstore-browser-state-set.
Created attachment 428654 [details] [diff] [review] patch plus test v1
See bug 542946 comment 5 wrt the test name...
Created attachment 432097 [details] [diff] [review] same as above, renamed test files as agreed same as above, renamed test files as agreed, carrying forward r+ sr+ from Neil, got approval for renaming on meeting over IRC.
Pushed as http://hg.mozilla.org/comm-central/rev/2c611970cf52 - thanks for your work!