[solardev]

For cross-tab communications, there are better APIs, like https://developer.mozilla.org/en-US/docs/Web/API/Broadcast_C...

For user-driven automations, something like Tampermonkey would be way better (and safer, since they can be domain-limited).

I can think of no reason why a regular user would want to allow tabs to execute each other's code... that just seems like a setup for self-XSS attacks by people who don't know any better :(

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edit: Sorry, re: the second part of your comment, I misunderstood what you meant. Like if you wanted to purposely script multiple identical tabs at the same time.