Affected versions

• 84.0b4, 85.0a1(2020-11-24)

Affected platforms

• macOS 10.15,

Steps to reproduce

1. Launch Firefox, access any page (such as reddit);
2. Open Print Preview;
3. Click on Landscape mode; - optional;
4. Press the TAB key until focus ring reaches the page;

Expected result

• focus ring selects the page;

Actual result

• the focus ring does not expand over the full page;

Regression range

• fairly hard to get a range since it's not jumping in the page after and at some point;
• First bad: 2020-11-05;
• Last good: 2020-11-04;
• Pushlog: URL
• Potential regressor: mozregression points toward bug 1617369;

Additional notes

• issue can also be triggered by holding down the TAB button for around 5 seconds;
• S4 as suggested severity;
• attached recording to illustrate the issue.