Have a closer eye on FlyWeb regarding proxy bypass
As mentioned in legacy/trac#19048 (moved) FlyWeb (https://wiki.mozilla.org/FlyWeb and https://hacks.mozilla.org/2016/09/flyweb-pure-web-cross-device-interaction landed but it is behind a pref (dom.flyweb.enabled
is set to false
). Nevetherless, it is scary enough that we should make sure that it is really disabled.