> For each message to be sent to or received from a worker we need to convert it to a string.

Strange, according to MDN data sent to web workers needs only be deep clone-able[1]. Is this non-standard Gecko behavior?

> aMessage: This may be any value or JavaScript object handled by the structured clone algorithm, which includes cyclical references.

[1]: https://developer.mozilla.org/en-US/docs/Web/API/Worker/post...