Developer here who works on the printing support. This looks like a bug in Firefox that we need to fix but it's difficult to work through issues like this on support.mozilla.org. Would you mind creating an account on https://bugzilla.mozilla.org/ and opening a bug report there so that it can be investigated properly?

Thanks for your reply. I have done as you asked and created a new Bug Report - Bug 1666914.

Thank you!

Hi CSH, could you take a look at this preference:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

(2) In the search box in the page, type or paste paper_data and pause while the list is filtered

Firefox should list the value for all of your printers. My general understanding is:

• 1 => letter
• 9 => A4

If your printer with A4 paper does not have this value set to 9, try editing it:

Double-click the preference to display an editing field, and change the value to 9 then press Enter or click the blue check mark button to save the change.

Any improvement?

More info on about:config: Configuration Editor for Firefox.

Hello jscher2000

My current printer value was 9 and I checked that the problem still existed. I noticed that two old printers were showing 1 and 6. I tried changing to both of these and the problem persisted. I changed my current printer back to 9 and surprisingly it seems to have cleared the problem.

I won't show the problem is solved for now, I am going to carry on using the printer to see whether this is a permanent fix, or if it reverts to again. I will aslo update my Bug Report on Bugzilla.

Thanks very much for your helpful reply.

CSH

@jscher2000 For your future reference after Firefox 82 is released, note that as of Firefox 82 the *paper_data* prefs will no longer be recognized/used by Firefox. They will be replaced by the *print_paper_id* prefs. I *think* (I haven't checked) that the values stored in the new prefs on Windows will be the same system paper IDs as the values that were stored in *paper_data*, but the prefs will be a string instead of a number. On macOS/Linux the values stored will be semi-human readable system paper IDs, again as strings.

As a bonus it may also be useful to know that the system paper ID numbers on Windows can be inferred from the comments at the end of each line in this source code. DMPAPER_LETTER starts at 1, and the others count up from there.

Hello jscher2000

Just to update my post of 24-09-2020, I have been using my printer for several days now and this problem has not happened again.

Following your suggestion of 23-09-2020, the value for my printer under paper_data was already 9, but trying other values and then changing it back to 9 appears to have somehow cleared the issue.

I don't understand this, but it worked. So thank you very much for replying with a helpful solution.

CSH