Backport patch for bug 1444532 to Tor Browser stable (7.5)

We have some crashes that might fit to the problem fixed in https://bugzilla.mozilla.org/show_bug.cgi?id=1444532 (see for instance latest comments in legacy/trac#22158 (moved), maybe even legacy/trac#20390 (moved)). We should try to backport that patch to Tor Browser 7.5.