Affected versions

• 82.0a1 (2020-08-28)
• 81.0b3

Affected platforms

• Windows 10
• macOS 10.14
• Ubuntu 18.04

Steps to reproduce

1. Launch Firefox
2. Make sure print.tab_modal.enabled is set on true
3. Open any page
4. Hit Ctrl +P
5. Make some changes (eg. set scale to 40, set color to black and white)
6. Set print.tab_modal.enabled on false
7. Open print preview (or print to paper for mac)
8. Observe the outcome

Expected result

• The changes made with the pref on true are not kept

Actual result

• The changes made with the pref on true are kept

Regression range

• Not a regression, reproducible with 81.0a1 (2020-08-07).

Additional notes

• Issue persists after restart as well.

Suggested severity

• S3

I kind of expect the result you reported, and don't believe many people will be switching to and from the new UI that often, so calling it a P3/v82.

On the same note, but with a more plausible scenario I’ve determined an undesirable scenario:

1. Launch an older Fx (without the new Print modal implemented)
2. Open Print preview for any page
3. Set Custom scale to >200 (eg. 300)
4. Update Fx
5. Hit Ctrl + P
6. Observe the scale field

Actual result:

• The scale kept the previous value.. Although the red border is present, there is no warning message, modal options can be accessed, Print preview is scaled to a larger value than intended for the new UI
• Although Print can be clicked it has actually no response
• Changing the destination to Save to pdf turns the modal options greyed out
• Without interacting with the scale value, the issue persists on every new tab and the print preview displays every content to the corresponding value (here 300%).
• Changing the scale to Fit to page width resets the value to 100 (while greyed out)

Yeah, that's fair. Everyone will have to upgrade from an older version sometime, right?

[Moving front-end printing v82 bugs to v83.]

(Moving bugs to 86, part 2.)