Affected versions

• 84.0a1(2020-11-11), 83.0;

Affected platforms

• macOS 10.15, Windows 10;

Steps to reproduce

1. Launch Firefox and access about:telemetry
2. Access any of scalars/enviromentData/Raw json and expand pages so scrollable content is enabled;
3. Open the print preview;

Expected result

• preview should extend to as many pages needed to show whole content;

Actual result

• preview is limited to only 1 page (most likely print as well)

Regression range

• first bad: 2017-06-27;
• last good: 2017-06-27
• Pushlog: URL;
• checking on older builds, the preview was extended to 2 pages, second one being blank;

Additional notes

• S4 as suggested severity, since it's more or less an edge case;
• attached screenshot to best illustrate the issue;
• looking with :vlucaci around pages revealed that some internal about: pages are also as well:
  • about:networking#http
  • about:preferences
  • about:debugging#/runtime/this-firefox
  • about:policies#documentation

The severity field is not set for this bug.
:mats, could you have a look please?

For more information, please visit auto_nag documentation.

The issue here is that the page as a whole isn't what is scrollable; the scrollable content is within an element that is sized according to available space on the page, and its overflow doesn't "escape" to appear on subsequent pages.

More generally, it's not clear to me how printing should deal with the contents of scrollable areas on the page. Attempting to expand the element so that all its content becomes visible for printing (and potentially gets fragmented across multiple pages) could totally disrupt the rest of the page layout.

I think figuring out an approach to printing pages with scrollable areas is more of a potential enhancement (if we can design a workable approach) than a bug.

Sounds like we're handling this correctly to me. We should fix this with a @media print rule for about:telemetry (and other about: pages).

https://hg.mozilla.org/mozilla-central/rev/1ce1ac399abc

Initial issue - patch verified with 85.0b4.
Filed a followup bug for about:policies#documentation and about:preferences; pages that still show the issue.