[entuno]

Trust is a about the author, not the code.

Open source is a bare minimum, although even that's not worth as much given how much harder it is now to load extensions that you've compiled yourself.

But those features you're talking about sound like they need extensive privileges within the browser. And while your extension might do what it says today, what's stopping you sticking a load of malware and adverts in there tomorrow? Or selling it to someone else who does?

If the author is an established person whose been known for years to develop good quality extensions and not sell out, then that gives some assurance. If it's an organisation like the EFF, even better?

But a random anonymous person making their first extension? No chance.