** Steps to reproduce:**
Go to an email that contains a multi-level thread and open the email.
OR
Load TC: https://bugzilla.mozilla.org/attachment.cgi?id=9228714
OR
Load form PDF: https://bug1671648.bmoattachments.org/attachment.cgi?id=9182033
Bring up in Print Preview (cmd+p)

** Actual results:**
Indentation is NOT visible in print preview.

** Expected results:**
Indentation is visible in print preview.

** Additional information:**

• This issue occurs on a specific Win7 system and not on another.
  About:support information of the affected system will be attached.
• This issue no longer mentions the use of high contrast. Please remove the "access" keyword if the case.

about:support info from the affected system

When attempting to zoom in using the trackpad, the little gray indentation line appears and disappears even though no actual zoom is observed in the print preview.

This means it will not be missing from the actual print, and it is only an issue of the print preview. Not sure whether we should consider lowering the severity or actually rendering the issue invalid. I'll leave that to you.

Yeah, I think this is ~invalid given the resolution. However the fact that it appears and disappears makes me think there's some inconsistency on how we snap / render zoomed-out borders, so probably moving to graphics is the right thing to do.