https://github.com/potch/corsica-extension/tree/master/icons is the corsica addon icon. I'm checking to see if that's being caused by another thing.
Bug 1557156 Comment 5 Edit History
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https://github.com/potch/corsica-extension/tree/master/icons is the corsica addon icon. I'm seeing the same thing with the corsica addon icon regardless of if I'm in light or dark mode on MacOS.