I'm marking this as a duplicate of Bug 1812834 because the latter would cover the describe use case, and this bug is set to P5 and doesn't mention what missing API is preventing extensions from implementing such a feature.
Bug 1811584 Comment 2 Edit History
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I'm marking this as a duplicate of Bug 1812834 because the latter would cover the described use case, and this bug is set to P5 and doesn't mention what missing API is preventing extensions from implementing such a feature.