Isn't installing extensions considered extremely dangerous?
These extensions usually have full access to the DOM, so they can do everything they want to.
So their question is very much warrented: installing as new extension should always be well considered.
You cannot universally answer the question "how much of a threat are chrome extensions".
firefox addon store is very much better in that regard. Anyway, this makes me feel like you don't know about gorhill and UBO? that is actually recommended for sane internet browsing on any browsers.
As i often say, surfing the internet in a browser without UBO feels like having unprotected sex. Fun but dangerous.