bug(list): firefox renders action list focus state on 3 sides instead of all 4 sides

[zarend]

Reproduction

Use StackBlitz to reproduce your issue:

• Components: https://stackblitz.com/fork/components-issue
• Harnesses: https://stackblitz.com/fork/harness-issue

Steps to reproduce:

1. Enable high-contrast mode in Firefox
2. Open the dev-app in firefox and navigate to the list demo
3. Navigate to the Action List demo
4. Hover over "Outbox"

Expected Behavior

Displayed dotted outline on all four sides of "Outbox"

Actual Behavior

Displays dotted outline on only the top, left and right side of "Outbox"

Environment

• on master at commit 760b4564fa41f1d13d4e07e9cba4fa3440284af7
• macOS big sur 11.5.2 (20G95)
• Firefox 91.0.2 (64-bit)

This does not happen on Chrome.

Additional Notes

This came from an internal bug report found during a11y testing.

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