I suspect https://hg.mozilla.org/mozilla-central/rev/d54f1666473acafb01bbcb6d50846a8cf6a379d2 that removed border color and then set border-width on non-proton
Bug 1699821 Comment 5 Edit History
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I suspect https://hg.mozilla.org/mozilla-central/rev/d54f1666473acafb01bbcb6d50846a8cf6a379d2 that unset border-width on non-proton