Simple measurement sessionRestored does not measure at all the time until session is restored. We need a better name. sessionRestored is updated when we receive notification of sessionstore-windows-restored. In turn, this happens once Session Restore has determined that all windows (*not tabs*) have been restored. Roughly speaking, that's when the main process has done all it can do without having to wait for the content process or the in-process framescripts. The story is of course a bit more complicated, because there are at least 5 different paths that can lead to that notification, but it's the general idea.