Firefox locks up gnome-shell
Since my upgrade from Fedora 26 to Fedora 27 I get complete hangs of gnome-shell now and then. The triggering factor seems to be Firefox somehow as I've been browsing every time it happens. At this point Firefox's Web Content process is consuming loads of CPU. Killing it does not restore functionality to gnome-shell though. And gnome-shell doesn't respond to any signal, so only SIGKILL gets things up and running again.
strace shows it wedged with some futuxes. I've included a gdb bt of all threads: gnome-shell-hang.txt