I don't think this needs to be tracked. This is only a regression insofar as we had a bug in how we were serializing onMessage responses. We're using Structured Cloning for every other place to forward extension-provided data, except for onMessage return value which is just returned as a result of the IPC message. Previously, with MessageManagers that had a fallback to JSON if standard serialization throws, which we don't actually want. The fix here is to explicitly use Structured Cloning, and throw with a clear error message. So we don't actually plan to change behavior here, I'm marking it as fix-optional for 82.
Bug 1657384 Comment 8 Edit History
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I don't think this needs to be tracked. This is only a regression insofar as we had a bug in how we were serializing onMessage responses. We're using Structured Cloning for every other place to forward extension-provided data, except for onMessage return value which is just returned as a result of the IPC message. Previously, with MessageManagers that had a fallback to JSON if standard serialization throws, which we don't actually want. The fix here is to explicitly use Structured Cloning, and throw with a clear error message. Since we don't actually plan to change behavior here, I'm marking it as fix-optional for 82.