It doesn't make any sense for us to show the option to quit PB mode in the jumplist menu if the permanent PB mode is active (see also bug 601253).
We support turning on the PB mode from within the preferences UI, so I think this should block 4.0 (especially since that it's a really easy fix).
Created attachment 480298 [details] [diff] [review] Patch (v1)
Comment on attachment 480298 [details] [diff] [review] Patch (v1) Wasn't sure if the open() change made sense, but I see we already disable Tools -> Stop Private Browsing when in permanent PB mode, so it's consistent with that.
Current latest-trunk always shows "Enter private browsing" entry in jumplist when permanent PM mode is enabled. Is that ok? Is that a regression? When firefox is closed and I select that entry, firefox will not open. Otherwise (when firefox is already open) nothing happens.