Don't allow MitM by Microsoft Family Safety in ESR 52

Firefox supports the Microsoft Family Safety "feature" now (see: https://bugzilla.mozilla.org/show_bug.cgi?id=1239166). We don't want this MitM opportunity. Probably just setting security.family_safety.mode = 0 is enough.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information