Firefox not always using http/3?


This is a little unrelated to Caddy perhaps, but I notice that it does not often connect to my site over HTTP/3, but uses HTTP/2 quite a lot. Using Opera browser (Chromium based) it always works. Strangely, sites like and show that FireFox uses HTTP/3.

Is this a known problem, or should I try to debug it and report it to Bugzilla?

ps. I’ve read about qlog. Is this something that I enable in FireFox, and how would I go about logging my session using it?

I wouldn’t really be able to say, I don’t think Matt would know either. The HTTP/3 implementation isn’t maintained by us. We’re using this library:

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I’d say it’s s Firefox problem. Looking at their bugzilla there seems to be quite a few issues still.

One thing, which might be intended, is that the alt-svc cache is dropped so when you’re dev tools with no cache, only http2 can be used.


Hi again.

I take it all back :smiley:

It seems that Caddy simply stops responding on http/3 after a while. Not even curl --http3 can connect. If I stop (ctrl-c) and start Cadd (caddy run) it works as expected again. I did not see any errors in the logs either. Though they are quite long, so I will dig some more.

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Ah, that is definitely a mystery. Please contribute any additional info here:

We could use some help pinpointing that.

Thanks. I did. Hopefully we can debug och pinpoint the cause of the problems.

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