When we added the View menu pane options in 3aeef69ad3, we removed
automatic reopening of the panes on startup, since the View menu is more
discoverable than the narrow collapsed splitters. Unfortunately we're
now getting many reports of people not knowing where their panes are.
It turns out the View menu pane options in 5.0.76 are actually broken,
so it's not a great test, but enough people are doing this by accident
and enough of them don't seem to be finding the View menu options
(broken or otherwise) that I think it's better to return to reopening
the panes. We can always add a hidden pref to change that behavior, but
no one has complained in years, so it's probably not necessary.
4f9e4bee86