2cd74a0e96
bug 1717765 changed the behavior for non-SHIP too, and https://searchfox.org/mozilla-central/rev/d0c13bb2a9c3a9ab6f5eb5a23230161928b079d9/docshell/base/nsDocShell.cpp#6922 seems to rely on the old behavior. We need to have DocumentViewer always when restoring from bfcache, and non-SHIP doesn't deal with failure cases well. No test for this (at least not yet). Differential Revision: https://phabricator.services.mozilla.com/D225409