Very curious, indeed. Thanks for sharing a concrete video of the repro.
Could you run another snippet to get a more readable form of the listener data for us?
function convertNestedMap(m) { const res = {}; for (const [k, v] of m) { res[k] = typeof v?.has === "function" ? convertNestedMap(v) : v; } return res; }
JSON.stringify(convertNestedMap(WebExtensionPolicy.getByID("admin@fastaddons.com_SendTabToDeviceEnhancer").extension.persistentListeners), null, 2)