I was part of the pilot [0], and enjoyed the process. It didn't cost anything, and they only requested random surveys on the service.

My extension just sets the default search engine to Runnaroo, and I don't promote it much because people can just do that through the browser, but it was nice to get some increased exposure and I did notice an uptick in downloads, especially initially.

In general, I'm all for Mozilla testing different monetization strategies to offset some of their reliance on Google.

[0] https://addons.mozilla.org/en-US/firefox/addon/runnaroo/