The performance has been shown not to hold for adblocking extensions (https://whotracks.me/blog/adblockers_performance_study.html), and there are many other problematic webextension APIs w.r.t. privacy.
The solution to these issues should be institutional, not technical. Google should impose performance constraints on extensions, and audit what data extensions are sending home. However, looking at the rampant malware on all their stores, this is something they're unlikely to do, so instead they'll nerf extension's capabilities.
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