This is a case where menulist.css has more specificity than the bookmark panel style. Might be worth to start using :where() to prevent un-expected regressions from higher specificity of selectors :) Or fixing the consumers themselves.
Bug 1699553 Comment 0 Edit History
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This is a case where menulist.css has more specificity than the bookmark panel style.
This is a case where menulist.css has more specificity than the bookmark panel style: https://searchfox.org/mozilla-central/source/browser/themes/osx/browser.css#457-464
This is a case where menulist.css has more specificity than the bookmark panel style: https://searchfox.org/mozilla-central/rev/cc4a17cea338fe236626d838ca96e9bf6a775675/browser/themes/osx/browser.css#457-464