This probably needs fixing in all repos.
gtk2 appears not to have CUPS integration compiled in.
This makes printing very difficult with firefox and seamonkey, and may be why chromium-browser locks up if printing is attempted.
I tried editing .gtkrc-2.0 as described in the following bug report. I can remove file and lpr from the print list but cannot get CUPS printers
to be seen.
https://bugzilla.mozilla.org/show_bug.cgi?id=460318----Edit----
I checked the gtk3 Apps, and their priint dialog box shows CUPS printers.