Firefox 45.1.0esr is broken with mingw-w64
The fix for https://bugzilla.mozilla.org/show_bug.cgi?id=1255627 landed on 45.1.0esr but breaks our Windows build. Jacek was fast again and got already a fix into mozilla-central (see: https://bugzilla.mozilla.org/show_bug.cgi?id=1263653). We should backport that one.