Firefox: `CloseNow` returns "A parameter or an operation is not supported by the underlying object"

Hi there, I noticed in Firefox WASM calling `CloseNow` returns an error:

> A parameter or an operation is not supported by the underlying object

This can be fixed by instead calling `Close(websocket.StatusNormalClosure, "some reason")`.

Since `CloseNow` is just an alias for `Close(websocket.StatusGoingAway, "")` my guess is that the empty reason value is being rejected by the browser,

Start by tracing the CloseNow alias and the Close call in the Firefox WASM path, then reproduce the reported error in Firefox. Done means CloseNow no longer returns the unsupported-operation error while preserving the intended close behavior.

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