I don’t like CUPS but it’s a necessary evil on OpenBSD, at least if you want to be able to print from Firefox. It’s OK when it works but I’ve found that printing sometimes stops working for no apparent reason, and CUPS is so complex that you can chase the solution for hours or days.
On this occasion I was still able to put the data to be printed into the queue but CUPS wouldn’t print it. The solution I found was to reinstall the printer (Brother HL-5030DN) and to use the Backend resource to set the printer’s local IP address as backend:
I could then print from the command line but printing from Firefox still didn’t work. To fjx that I needed to modify about:config.
Method: Type about:config into the address bar of the browser. Accept the warning and promise to be careful. Once you are in about:config, type ‘printer’ in the search panel at the top of the screen. This brings up an entry where you can type the same IP address that you used in CUPS. This shoud give you printing in Firefox.