Needs an option to "do not block" as default, instead of having to whitelist websites one by one. So it would *only* block the websites in a blacklist, instead of only *not* blocking whitelisted ones.
Other than that, I really like that it's easy to disable, requires few permissions and works well.

Edit: Fair answer. Upped my rating to 4. Honestly, my real issue is that it keeps blocking important popups like "Login with Facebook" buttons, and I have to keep setting up those sites one by one. Not sure what'd be the best solution for that.