I'm not aware of any JavaScript sandbox widely regarded as flawless. AdBlock is one thing, but I have no qualms about not running arbitrary scripts that aren't

I'm not aware of any JavaScript sandbox widely regarded as flawless. AdBlock is one thing, but I have no qualms about not running arbitrary scripts that aren't even hosted by people I know and trust. If a publisher doesn't bother to use <noscript> or <iframe> to show me an ad anyway, it's their own oversight.