Affected versions

• Firefox 86.0a1 (BuildId:20201218095607)

Affected platforms

• Windows 10 64bit
• macOS 10.14
• Ubuntu 20.04 64bit.

Steps to reproduce

1. Launch Firefox.
2. Open a random webpage (non about/local page).
3. Open a different tab and access the about:support page.
4. Hit CTRL + P on the about page.

Expected result

• The print preview is displayed for the about page.

Actual result

• The print preview is displayed on a different tab.

Regression Range

• This seems to be a regression:
• Pushlog: https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=6307b67c66ffa34fdbdb8481cc95f58a5cc8df29&tochange=84d74806a0f714937f8de369fef595c5220f9381
• Potential regressor: Bug 1670122

Notes

• For further information please observe the attached screencast.
• It seems that the only way to trigger the print preview for the local pages is by closing all the other tabs.
• This issue is reproducible with both Fission enabled and disabled.
• [Suggested Severity] I think that S3 fits for this issue.

Hi Emma,

It seems that mozregression pointed out Bug 1670122 for causing this regression.

The pushlog from the bug's description was generated after a second bisection. At first, It gave me this one.

I also can confirm that this issue is not reproducible with the last release without & reproducible with the first release with builds from here.

Can you please take a look?

Thank you!

https://hg.mozilla.org/mozilla-central/rev/eb3ff7d6b951

Moving things to 88, cause we're mostly on Proton these days…

This issue is verified fixed using Firefox 86.0 on Windows 10 64bit, macOS 10.13 and Ubuntu 20.04

Mark, I'm trying to understand this code. I guess the wrong browser comes from:

<command id="cmd_print" oncommand="PrintUtils.startPrintWindow(gBrowser.selectedBrowser.browsingContext);"/>

Why is gBrowser.selectedBrowser.browsingContext the wrong thing when an about: page is open and focused? I'd like to add a comment to this code explaining what's going on, because it's not at all obvious.

I misread this code. 'gBrowser.selectedBrowser.browsingContext' is the right thing in that case and Services.focus.focusedContentBrowsingContext is the wrong thing. That's the wrong thing, presumably because focusedContentBrowsingContext isn't set to a content process browser such as the one for about: pages.

So I guess my real question is why we override the passed BrowsingContext with Services.focus.focusedContentBrowsingContext? We appear to have started using that it https://phabricator.services.mozilla.com/D94467 so it seems the answer is "to get the correct BrowsingContext when printing 'selection only' and printing wasn't initiated from the context menu."

FWIW I filed bug 1748846 for this.