1762982 - Print viewport width is a bit smaller in Firefox vs. other browsers, causing different media queries to match (especially around the common 767px threshold)

Status: RESOLVED INVALID

(Core :: Printing: Output, task)

Description

[Daniel Holbert [:dholbert]]

In bug 1759775 comment 10 (and bug 1759775 comment 13), it came up that @media (max-width:767px) { CSS media queries seem to match in Firefox but not-match in other browsers, when printing to portrait-oriented US Letter paper with default settings.

This is due in part to our default page margins being slightly larger than other browsers (I think). I'm not sure if that's the full story or if there's anything additional that makes our resolution slightly different.

In any case: given that...

• 767px is a common media-query threshold (googling for "767px" turns up lots of media query discussion)
• portrait-oriented US-letter paper is a common print target
  ...it seems like we may run into other compat issues where Firefox produces different print output than other browsers simply due to falling on the opposite side of this 767px threshold.

I'm filing this bug to track this category of issue, & for any investigation/action that might result.

Comment 1

[Daniel Holbert [:dholbert]]

(In reply to Daniel Holbert [:dholbert] from comment #0)

In bug 1759775 comment 10 (and bug 1759775 comment 13), it came up that @media (max-width:767px) { CSS media queries seem to match in Firefox but not-match in other browsers, when printing to portrait-oriented US Letter paper with default settings.

Sorry, this turned out not to be correct.

I thought it was correct based on my partial analysis of bug 1759775, but when I created a reduced testcase, I found that the media query resolved the same way in Firefox and Chrome (both are less than 767px with default print settings & portrait-oriented US Letter paper).

It turns out there's another piece that's necessary to trigger the bug, from an external stylesheet in bug 1759775: @page { size: a3 }

To avoid confusion, I'm just going to close this one as INVALID and I'll file a new bug with a testcase that actually demonstrates the issue (with size: a3)