Sorry for the delay here. Extensions are great. There's plenty of examples in this space that have become big companies (Loom, etc.) Chrome also has the highest market share, and even upstarts like Arc Browser are built on Chromium so they work on those platforms. The only real downside is that they're difficult to test and deploy frequently (there's always a lag between pushing a new update and it being deployed, unlike when you own your own release schedule) so it's annoying to constantly have to discover when your extension was updated.
P.S. It's ms. ceo ;)