I made http://feeder.co , a Chrome extension to simulate Firefox's RSS live bookmarks back in 2010. Now it has 500,000 active installs on Chrome and our cloud hosted service is netting around 1500 USD each month after costs (1700 subscriptions). Me and my twin brother have had it as a passive income thingie for years. After a failed attempt at selling it (SaaS metrics are NOT easy) we met a guy who saw some potential…
Pardon my ignorance: but how one actually earns money with chrome extensions?
Then, the user, in fact, pays only for using the back-end API. The front-end, of course, is like a website, """open-source""".