Affected versions

• 85.0a1
• 84.0b8

Affected platforms

• Windows 10
• macOS 10.15
• Ubuntu 18.04

Steps to reproduce

1. Go to https://search.yahoo.com/
2. Ctrl + P on the page
3. Expand More settings and select Print backgrounds

Expected result

• The background is centred

Actual result

• The background is cut off and right shifted

Regression range

• Pushlog: https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=fe58cbb7b54668bb9bdfb13922ffbd60394b1199&tochange=049d66db392d8ac74b262ab22a2aab62231fad5d

Additional notes

• Not reproducible on Chrome
• Reproducible with different paper sizes, scales, destinations
• Issue visible with the old UI
• Note that on Landscape mode the background is moving on scroll, probably due to background-attachment: fixed

Suggested severity

• S3 since other pages can be affected

This seems to work for me now?

(In reply to Emilio Cobos Álvarez (:emilio) from comment #1)

This seems to work for me now?

This is still reproducible on my end with Fx 85.0a1 (2020-12-14) on Windows 10 and Ubuntu 18.04.

Anca: what about now, particularly on Nightly?

(In reply to Jonathan Watt [:jwatt] from comment #3)

Anca: what about now, particularly on Nightly?

Still reproducible on Fx 86.0a1 (2021-01-25).

This seems to actually be a WebRender bug.

On my system, I can reproduce in Nightly 2021-02-01 but not in 2021-01-01 (using fresh profiles) and mozregression gave me this break range:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=9226bc3ca03cb41a7ff3047d4c3029eba25b3c38&tochange=677276fcfc39b39dd806cf86cd58532f2215417c

...which is " Bug 1689189 - Ship Software WebRender to users with large screens in nightly and early beta".

I can reproduce similar breakage in Nightlies from a year ago, with the legacy print-preview, in a profile with WebRender force-enabled (gfx.webrender.all = true). So this also isn't software-webrender-specific; it's just webrender-specific.

(In reply to Daniel Holbert [:dholbert] from comment #5)

This seems to actually be a WebRender bug.

...though actually: even though this is WebRender-specific, this is probably just a bug in our printing display-list code which happens to be revealed by WebRender.

(I ran into & fixed one such issue a little while back, in https://hg.mozilla.org/integration/autoland/rev/7c46b561db00 )

Here, it look approximately like we're neglecting to apply one of the print-preview transforms, when drawing the background-attachment: fixed background image.