Thanks for writing the post, I built a moderately popular extension in 2012 "Twitcher" for switching between twitter accounts (https://chrome.google.com/webstore/detail/twitcher-twitter-a...).

I've toyed with different monetisation strategies over the last couple of years, I even conducted a 6 month survey of what people would be willing to pay. In the end I decided I couldn't justify charging for it and a few months ago I rolled out a "pay-what-you-want" model like AdBlockPlus, during the A/B test on 20% of users I generated just over $100 dollars in the first 2 weeks, then basically nothing - so the annual/monthly model is attractive!

I like the idea of keeping it open source, then those who don't want to pay can still use it - think I may follow your model :)