I didn't notice that I had left SW WR enabled. :) I made a Twitter video fullscreen, saw bug 1657443 and got this main process crash.

This bug is for crash report bp-1aa65d47-17e5-4b4e-b1fd-9644e0200807.

Top 8 frames of crashing thread:

0 libc.so.6 __memmove_avx_unaligned_erms 
1 libxul.so Composite gfx/wr/swgl/src/gl.cc:4127
2 libxul.so std::sys_common::backtrace::__rust_begin_short_backtrace src/libstd/sys_common/backtrace.rs:130
3 libxul.so core::ops::function::FnOnce::call_once{{vtable.shim}} src/libcore/ops/function.rs:232
4 libxul.so <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once src/liballoc/boxed.rs:1017
5 libxul.so std::sys::unix::thread::Thread::new::thread_start src/libstd/sys/unix/thread.rs:80
6 libpthread.so.0 start_thread ./nptl/pthread_create.c:477
7 libc.so.6 clone 

Marking as S3 as this isn't enabled anywhere yet.
Lee, want to look at this?

SWGL video is still in flux, and given the age of this bug, I am not entirely sure video was really working all that well back then. I will leave this bug open to catch other reports of this signature, but for the moment it doesn't seem to be a widespread problem.