Is your extension collecting email addresses? I got an email after trying it out.
When I started this project I wanted the onboarding experience to be as simple as possible, i.e. no annoying sign up stage. I wondered whether this approach would lead to lots of questions like yours: in fact, I think less than 5 people have asked about this since 2015. My sense is that, on balance, most people benefit from the "install = sign-up" flow.