For compatibility with our old print UI, and with Chrome, we need to add support for setting custom margins to the new print preview UI.

According to bug 1663344 comment 32, on Windows users cannot use the "Print using system dialog..." escape hatch to adjust margins as they can on macOS. I don't think we can ship to a substantial number of users without some sort of ability to continue to set custom margins, so I think that makes this a P1. :-/

I guess this should be targetting v82 if we're planning the experiment for that.

Just looking at the telemetry ( https://sql.telemetry.mozilla.org/queries/74390#186893 and https://sql.telemetry.mozilla.org/queries/71985/#180650 both switched to 'beta' ) it looks like before the pref got turned off on beta we had the following for Windows Beta:

• 1-2 million prints per day
• maybe up to 7000 changes to margins per day

So it was maybe every 1/200 prints that a user was dissatisfied with the margins and wanted to change them? That seems a bit high to expose this to a large number of users without any way for users to provide their own margins. :-/ I'm particularly worried about the papercuts adding up. What do you think, Blake?

Yeah, this definitely seems like something we want (although 0.4% isn't that much), but I would be fine running the experiment in 82 without it, as long as we were reasonably confident we could get it in for 83. Let's leave it as a P1, and see if we can get to it, and if we do whether we think it's too complicated to uplift or not.

https://hg.mozilla.org/mozilla-central/rev/8d32fad4431d

Comment on attachment 9176435 [details]
Bug 1664570: implement custom margins in new print UI

Beta/Release Uplift Approval Request

• User impact if declined: The users will not be able to set custom margins, which would be a regression from the old print UI
• Is this code covered by automated tests?: Yes
• Has the fix been verified in Nightly?: No
• Needs manual test from QE?: Yes
• If yes, steps to reproduce: 1. Open print preview with print.tab_modal.enabled set to true

2. Set margin to "custom"
3. Observe that you can change custom margin values

• List of other uplifts needed: None
• Risk to taking this patch: Medium
• Why is the change risky/not risky? (and alternatives if risky): There is one fluent string, but this change is necessary
• String changes made/needed: Fluent string is introduced

Do we still want to pursue uplifting here despite the regressions found in nightly so far?

This was also causing errors that are fixed in bug 1663503

Cancelling the uplift request, as this feature will just land in 83

Confirming this issue as verified fixed on 84.0a1(20201019213835) and 83.0b1(20201019162914). Verified using macOS 10.15.7, Win10x64 and Ubuntu 20.04.