I needed a Chrome extension after they inexplicably broke backspace navigating backwards (it literally has the same icon as the backwards UI button). That extension needs to inject a script on every. single. website.
It's like Google is spending millions upon dollars building convoluted sandboxing security features, and there is a place for that in protecting us from code execution. But then everyone is pushing for "apps on the web" and here we are with random extensions that can do everything. And they do: lots of them make money through selling your browsing history.