Hi! Thank you for your review. Which permissions are unnecessary?

Unfortunately, in order for Rikaichamp to be able to present pop-ups on the page it requires access to that page's contents. Web extensions do not provide any more fine-grained permissions that that. As far as I can tell, it's impossible to create a pop-up dictionary with fewer permissions.

The source code is available for audit and/or forking if you are concerned about misuse of those permissions.