I updated to Firefox 51 >> Firefox 52. I have firefox open though and after the install I restarted the browser and got no hint of any thing new except when I looked at the logs.
[tail of journalctl]
Mar 07 09:27:28 archdesktop systemd-coredump: Process 14430 (firefox) of user 1000 dumped core.
Stack trace of thread 14482:
#0 0x00007fa90a07af5f raise (libpthread.so.0)
#1 0x00007fa8fc62ed3d n/a (/usr/lib/firefox/libxul.so (deleted))