It turned out I had to explicitly reference `Ci.nsIDOMXULSelectControlElement` when calling implementCustomInterface. Passing `Ci.nsIDOMXULMenuListElement` along is not enough.
Bug 1518932 Comment 11 Edit History
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It turned out I had to explicitly reference `Ci.nsIDOMXULSelectControlElement` when calling `implementCustomInterface`. Passing `Ci.nsIDOMXULMenuListElement` along is not enough.
It turned out I had to explicitly reference `Ci.nsIDOMXULSelectControlElement` when calling `implementCustomInterface`. Passing `Ci.nsIDOMXULMenuListElement` alone is not enough.