This may happen after there has been a fault in the connection with the printer. CUPS stops the printer and you have to open CUPS, select printers and then, I think, Administration and Resume printer. You will be asked for a password - give your root password.
I entered the terminal data. It printed the test page, but not from firefox. I went into yast->printer. I found three printer configs, one said disabled. I deleted all the printer configs. I did “add printer”. That didn’t work. Again, I deleted all printer configs from yast->printer. I entered the terminal data. Now, the printer is working fine from firefox. Thanks.