User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:88.0) Gecko/20100101 Firefox/88.0

Steps to reproduce:

Always occurs when brother MFC5490CN is selected for printing

Actual results:

Running Ubuntu 18.4.05 LTS and Firefox 88.0.1. I have two networked Brother printers, an MFC5490CN and an MFCJ497DW. When printing to the MFC5490CN the new print UI dialog presents me with a list of metric page size options and nothing else. This only occurs in Firefox and not in other browsers and applications. The actual printer hardware settings are paper type "plain paper" and paper size "letter". All the about:config settings for both printers are identical except for the printer.printer_MFCxxxx.print_duplex setting since one printer can do double sided and the other does not. I have set print.tab_modal.enabled to FALSE so the system print UI comes up and all is well using that method.

Expected results:

I expected to see a paper size menu with US Letter, Legal, A6, A4, etc.

The Bugbug bot thinks this bug should belong to the 'Core::Printing: Output' component, and is moving the bug to that component. Please revert this change in case you think the bot is wrong.

Presumably this reflects the paper sizes we get from the CUPS driver for these printers. Emily, are there things we can do to investigate what's going on here and why the expected options aren't showing up?

Paul, could you attach a screenshot of what you see in the print dialog? I'm not sure if I'm understanding correctly what you mean by "list of metric page size options" ... does that refer to specific dimensions given in millimeters, or what form does it take?

The screen shot that was requested is attached above.

Thank you. What an odd collection of sizes... they don't generally seem to correspond to normal paper sizes (whether US or International) that I'd expect to see at all. So it's not just that they are lacking "human-friendly" names, they're strange sizes altogether.

Quite a few of them do look as though they're just a few mm smaller than a "standard" size, which makes me wonder if these are indicating the printable area (allowing for a narrow unprintable margin) instead of the actual sheet size. But that's not what is supposed to be listed.

For standard sizes (with an error of up to 4 points, about 1 mm) we use the PWG names and ignore the printer's name for them. For all other sizes, we just use the name that CUPS gives us. I would strongly suspect these are the actual paper sizes that CUPS is reporting.

I am a bit surprised that this only occurs in Firefox, although it's possible that other programs (including ones using GTK) are filtering paper sizes.

I'm inclined to think it is not a CUPS problem. The attached screenshot shows settings in the CUPS Web GUI for the offending printer. It has "Letter: for media size.

Same screenshot as the last but with complete media size menu shown.

Also on 114.0 (64-bit). Firefox print dialog box shows a myriad of too-small metric sizes which do not relate to what is in CUPS.