alt Hacker NewsIt doesn't even have to be malicious. I used a certain syntax highlighting theme for years, when out of nowhere the author pushed an update that rearranged all the colors. It was extremely disorienting. I forked the extension and reverted the change, so I know that one at least won't change out from under me anymore.
This is the thing I hate the most about "automatic updates" in general. I've disabled them and gone back to updating manually because the constant unexpected and unwanted UI changes finally broke a part of my soul. Unfortunately that is something that can't be done on the web, where major UI changes can be rolled out right in the middle of a session on you.