Good news everyone! Chromium is now perfectly usable on FreeBSD.
The longstanding hanging tab bug has been resolved. See also PR 212812 and this this FreeBSD forum post.

This was fixed in r337328 but is not yet available in 11.2-RELEASE. Fortunately there are temporary fixes too that you can use while waiting for the patch to be included in the next release.

First add this line to /etc/sysctl.conf:

net.local.stream.recvspace=16384

Second use a memory backed filesystem for the chromium cache. A script to do so was included in the chromium package, but it has since been removed now that a proper fix is coming in.

But if you want to do this manually, first ensure that ~/.cache/chromium directory exists and is empty. Then in /etc/fstab add this line with $USER changed accordingly:

md /home/$USER/.cache/chromium mfs rw,late,noatime,noexec,nosuid,-w$USER:$USER,-s300m 2 0

This will mount the chromium cache path on an UFS partition over a memory backed virtual disk.

I’ve been testing this for several days now and it works like a charm. Don’t forget to remove this workaround when you are past r337328 though.