#TIL: There are two ways to trigger use of the #HTTP3 / #QUIC #protocol in #webbrowsers:

#Chromium and #Firefox #browsers always start with #HTTP1 / #HTTP2, look for the “alt-svc” header in the response and switch to HTTP3 for subsequent requests if they find it. I knew that much.

But #Safari will instead query #DNS for the "#HTTPS" record and use that as a trigger. So it can work HTTP3-only for the cost of an additional DNS query. Unfortunately, the record type isn't widely supported yet.