(In reply to jscher2000 from comment #1)
(1) On Windows, Firefox populates the unwriteable margin area from my printer settings into about:config in the expected places.
(2) The new Save to PDF printer doesn't correspond to a physical printer so Firefox assumes an unwriteable area of 0 and prints to the edges of the paper. To override this, you need to use a different set of preferences (for example, setting them to 20 or 25):
Perhaps adjusting those preferences for your other printers could be a workaround while the issue of why Firefox is not properly reading the unwritable area from your printers gets sorted out.
Hi jscher2000, thank you for your feedback. As to your last reply, I'm the one who reported bug 1688823. I decided to report this issue as a new bug since my original bug report was confusing with the multiple results in FF's print preview interface, plus my own errors in attaching supporting documents and follow up comments. I thought it might be best to isolate and define the issue more clearly as a new bug, but if it was not appropriate to do that perhaps someone here could link them.
With regard to your suggestion to change the 4 settings for Mozilla Save to PDF print edges from 0 to 25, that would be a good thing to try. I disabled the print preview interface on both my computers as a workaround before getting your reply, so I will not be able to test your suggestion until I enable it again. Given all the trouble FF's print preview interface caused with my printer settings on both computers, I'm hesitant to do so.