AMO has access to installed extensions with window.navigator.AddonManager in ESR 52

https://bugzilla.mozilla.org/show_bug.cgi?id=1255039 and dependent bugs implemented a way in which addons.mozilla.org is able to gather data about extensions the user has installed (and be it just a "yes/no"). We don't want this.

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