After print/cups has been updated from 2.1 to 2.2.2, the printing queues vanished in www/firefox (50/51) and recent mail/claws-mail. Only print to file and default LPR are present. This happened out of the blue after updating the port. This is most prominet on all 12-CURRENT 9recent revision) and also on 11-STABLE.
It's possible that cupsd fails to start. This was fixed in 2.2.2_1.
cupsd is running. i can print with CLI commands, can examine the queues, can list them - I have that problem on several 12-CURRENT boxes even with the most recent www/firefox 9as of today). I must have to do with some informations not being properly propagated to the environment from which Firefox gets its informations (my naive guess). I tried to fiddle around with variables via Firefox' about:config, but with no success. The problem is not present on all boxes (same rev. of CURRENT, same rev. of Firefox). Maybe some garbage in the local user's .mozilla folder? I close the PR, because it is definitely not CUPS related.