Document reason for needing this

[michielbdejong]

Given that IIUC this registration server needs to be a Mozilla-hosted service, which is not ideal for security, privacy, as well as resilience reasons (the foxbox you own will become useless if we ever decide to discontinue this server). So we should document why we need this, and explain that those reasons outweigh the security/privacy/resilience implications, and which alternative options we discarded.

I think the primary reason is that unlike iOS, Windows, and OSX, Android does not support mDNS, right? Are there other reasons?

And I think one alternative option we discarded was adding mDNS support to Fennec, because this would still leave out users of other browsers on Android (notably the Android stock browser), right?

[michielbdejong]

We found another alternative for mDNS (putting local IP addresses in public DNS zones), which at the same time allows us to register a (second) LetsEncrypt certificate for the box and use that inside the local network.

We also found a way to scan a QR code from inside the browser (see webqr.com).

This means that nupnp is now only useful for people who don't want to click the getUserMedia "Allow" dialog, see fxbox/RFC#6 (comment).

So considering this documented now. :) Will reopen if our thinking about this changes in the future.