I just finished setting up CUPS and successfully made the Firefox to use CUPS for printing. At first I just installed cups-1.5.0p8 and change my /etc/rc.conf.local to add:
# Packages script to start (/etc/rc.d/)
At the bottom of the file. Now OpenBSD uses that instead of my previous posting and if I use my previous way, doing ps aux | grep cups will display bunch of cups threads being started. Recent way are much better.
So then when I open the http://localhost:631 (CUPS local page), I just add my network printer (HP Laserjet 9050dn) using socket://ip.address then downloading external driver from CUPS's website. Test printing went successful but when I want to print under Firefox, there's only Print to file and Print to lpr options with no CUPS printer. My office also have a Ricoh Aficio MP4500 printer but currently not working for me. Will try to figure this out later.
After searching for answers, I installed gtk+2-cups-2.24.9p0 with all of the dependencies. Restarting Firefox then checking the Print menu, I can now see the printer correctly. But when I tried to print, I get this pdftops failed error and printing queue stopped. So I went off to search for another answer.
Looking at OpenBSD's packages site, I saw cups-pdf-2.5.1 which might be the solution I was looking for. The packages is to print a file to PDF, but I have a feeling this can solve my printing issue. So I installed that, quit a lot of dependencies too then tried printing in Firefox. Wallah! Printing done, I'm happy so back to work. Later then.