This model is also a big performance win. The content blocker rules are compiled to an [efficient byte code format](https://webkit.org/blog/3476/content-blocker

This model is also a big performance win. The content blocker rules are compiled to an [efficient byte code format](https://webkit.org/blog/3476/content-blockers-first-look/ https://webkit.org/blog/3476/content-blockers-first-look/) which can be evaluated insanely fast (microseconds not milliseconds), compared to doing IPC and running JavaScript for each resource in a page.