They don't need to be crypto related. Any extension can include any code in it, so unless you have personally read all the code of what you extensions you are installing, you have no idea what they actually do, only what they claim to do. They could redirect you to phishing sites, steal your usernames and passwords, alter your clipboard, any number of things. We've seen people lost their bitcoin because of malicious code in everything from price tickers to ad blockers. There was even a case of clipboard malware being hidden in software which gave you custom backgrounds. Nothing to do with crypto, and seemingly innocuous, resulting in people losing all their money.

Your crypto activities should remain separately from your general online activities to help prevent things like this happening. The browser you use for crypto should be used for nothing else, and have minimal extensions on it - uBlock Origin, HTTPS Everywhere, Privacy Badger, and maybe NoScript if you can, is probably all you need. If you can use an entirely separate device for your crypto activities, even better. If you can't, then you should think about using a hardware wallet to protect against clipboard malware.