DebuggerServer.connectToChild is executed for every browser tab again when a new tab is opened. This also means that child.js is loaded more than once for a tab (a child process). This causes all the addMessageListener calls to be executed more than once. In the beginning these listeners used to be per-child, but now some of them are global. Registering them more than once is probably not harmful, but it would deserve some clean up. Honza
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