@ifreund @justine On my NetBSD VM, the problem seems to be in Mesa.

Nothing to do with blocking sockets.

What seems to be happening for me is that firefox is requesting a buffer to be displayed via Mesa. When that happens, Mesa does so using a SHM buffer which NetBSD rejects.

It's the same symptom which I've a work around for CoW, and is ultimately being tracked here in NetBSD:

https://mail-index.netbsd.org/netbsd-bugs/2023/09/20/msg079781.html

It doesn't look like kern/57622 has been merged yet.

So I suppose I could patch libmesa with a similar fix in CoW...

But I have some other things to do, and this isn't a problem with CoW, so....