Affected versions

• 86.0, 87.0a1(2021-02-10);

Affected platforms

• macOS 10.15, macOS 11

Steps to reproduce

1. Launch Firefox, access about:preferences#general
2. Scroll all the way down, click on the Settings button in Network Settings;
3. Scroll up/down inside the modal window;

Expected result

• scrollbar should not overlap with elements in modal;

Actual result

• scrollbar overlaps on both hover and idle state the content;

Regression range

• not a regression, issue visible with implementation of the window;
• First bad: 2017-07-18
• Last good: 2017-07-17
• Pushlog: URL

Additional notes

• attached recording to best illustrate the issue;
• probably best option would be to increase the default width of the window so the scrollbar would no longer overlap the set elements.

This is expected because of how macOS overlay scrollbars work, so kind of verging on wontfix. If it's straightforward to avoid this with some CSS I guess we could take a patch.