You may need to crank shared memory limits for chromium to work
properly under load:

# sysctl kern.shminfo.shmall=32768

Your default datasize might not be enough for v8 so make sure it
is more than 512M, so try to set it to 715M by doing:

$ ulimit -d 716800

or modify /etc/login.conf.

And opening lots of tabs may necessitate higher fd limits,
crank that via ulimit/limits.
