Don't you use Dropbox, Parse, Hootsuite, Mailchimp, CloudFlare or New Relic? It's a usual business model. Also, in my opinion, the vast majority of people would think "a free extension which one sees all of my movements on the internet says 'I'm gonna show you related advertising about your dragged items, hehe', what a horror story! I would rather pay 1$ or 5$ to it and feel safe myself.".