Affected versions

• 88.0a1(2021-03-24);

Affected platforms

• Win10;

Steps to reproduce

1. Launch Firefox, access the Customize page;
2. Drag a couple of buttons to the Overflow menu;
3. Close the Customize page;
4. Open the Overflow menu;
5. Press the UP-Down arrow keys on the keyboard;

Expected result

• items are selected, no artifacts displayed;

Actual result

• focus ring displayed on selection;
• with current Proton theme set up it's a white line inside the blue one(not ideal);

Regression range

• range set for when the focus ring started to have the dashed line:
• last good: 2019-04-22;
• first bad: 2019-04-23](https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=4c7eaf384b06cfda8314be34cd179ab46f271ccc&tochange=4b0811d7b8e1591d4e48a26bdb8666a1bc5ccf61);
• Pushlog: URL;

Additional notes

• with Proton-theme the Customize toolbar item is looking fine, the others still have the reported issue;
• attached recording to best illustrate the issue;
• most visible on proton-theme with dark themes set up.