I have written a couple dozen Firefox add-ons that have a combined userbase of 360,000 active daily users (assuming no overlap, so let's just say it's 300K). Naturally, I'd like to make some money off of these add-ons so I can justify continuing to develop more add-ons, which I greatly enjoy.
How would you monetize this situation? The problems I've come up against are:
1. People have an expectation that add-ons are (and should be) free.
2. It's hard to find a monetization option that makes sense for add-ons in different spaces. e.g., an RSS-related add-on has different logical monetization opportunities than a productivity-related add-on.
3. The only real opportunities out there right now for add-on developers involve selling premium add-ons (see #1) or adding some sort of advertising to the browser or the users' webpages (which feels scummy, and users typically don't like it).
So what would you do if someone gave you access to the browsers and eyeballs of 300,000 people every day?
If you'd like to make money on the side focus on platforms where people pay for things or that have a clearer path for indirect revenue. (The web, Windows, Apple, Android, Facebook, etc.)
I know it seems like the numbers are there and you're providing value but it would be an uphill battle. When focusing on income, your energies are better spent elsewhere.