In bug 1661157 it's noted that there can be a lot of blocking time where we show no UI. If it takes a while to collect printer data we should at least be showing a dialog that we're preparing the preview.

Show the print dialog as soon as the content is ready, rather than after
the printer and print settings have been retrieved, then focuses the first
form element.

https://hg.mozilla.org/mozilla-central/rev/1789be3b7d00

Reminder to request Beta uplift.

Comment on attachment 9172289 [details]
Bug 1661361 - Show print tab modal while waiting on printer data r?jamie,pbz

Beta/Release Uplift Approval Request

• User impact if declined: Long delays with no visual feedback when blocked accessing printer information
• Is this code covered by automated tests?: Yes
• Has the fix been verified in Nightly?: No
• Needs manual test from QE?: No
• If yes, steps to reproduce:
• List of other uplifts needed: None
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Test coverage of change, the codepath should only be hit by the print UI feature that's behind a pref.
• String changes made/needed: No

Comment on attachment 9172289 [details]
Bug 1661361 - Show print tab modal while waiting on printer data r?jamie,pbz

Approved for 81.0b6.

https://hg.mozilla.org/releases/mozilla-beta/rev/f87662899c06