The current theory is that some CDN/LoadBalancer updated its HTTP3 implementation and is now triggering a bug in the HTTP3 stack of Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=1749908#c21

It just happens that the usage data collection uses that CDN thus triggering the bug. But you can also encounter it by just visiting any other website served by that CDN.

I had too but it mysteriously re-enabled on all FF instances on various laptops and desktops here. I wonder when that happened.