Upstream a good editing, theming, tampering, blocking extension

[naturallymitchell]

https://github.com/schomery/policy-control is a good start

https://github.com/tophf/autopagerize is another good example of rule-based site actions

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https://gist.github.com/danharper/8364399 is a very basic idea of what's needed

https://github.com/sonerb/Chrome-Extension-Inject-JS-Example also

https://gist.github.com/uxter/50fb1c7011471442862bd921ec589a64 also

https://github.com/andre-st/chrome-injectjs also

https://chrome.google.com/webstore/detail/javascript-injector/ejnccfcackblkelbafbolcpjfpcmbplg?hl=en gives a very basic idea of what's possible and lacking when no site-specific / feature-specific rules & actions are available

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https://stackoverflow.com/a/9699373/8834980 is good

https://chrome.google.com/webstore/detail/web-developer/bfbameneiokkgbdmiekhjnmfkcnldhhm has some good UI examples