Loom https://www.loom.com/ started as a chrome extension.

Grammarly has done really well https://www.grammarly.com/

Streak CRM (YC S11) [https://www.streak.com/]

I think Hunter (https://hunter.io) started as a chrome extension

Password managers like LastPass (https://www.lastpass.com/) rely on their browser extensions for convenience and usability

I think that Rapportive started as a Chrome extension. I don't know much about the business but I believe the founder went on to start Superhuman.

Honey. https://www.joinhoney.com/

Moz (and friends) have a chrome extension.