Lex Friedman:

I’m a big fan of Safari Extensions. I’ve written several of my own, some of which I share with the Internet public. But because I’ve built those extensions, I’ve realized how easily a malicious developer could harvest all sorts of information about you, using a method that could sneak in and evade immediate detection.

Installed extensions can add any HTML to any page you surf to. And that’s where the danger comes in — and that danger is actually even worse than it first seems, which is already pretty bad.

Friedman’s extension is a little fugly – if he is using the extension himself, I am sure he will work on the aesthetics.