Yeah, I have a Firefox extension with around 50k installs, and get emails every so often from people offering to monetize it.

Here's an excerpt from a recent one, from Nick at NJB Brands Sales:

> We offer .50 CTR (per 1,000) traffic and can use each unique IP up to 10 times a day. There is no limitation to what we will purchase other than the cap per unique IP. We offer flexible payment options via PayPal, Bitcoin, WesternUnion or Check. Payment can be done every 1 day, 7 days or 30 days.