That's a good idea. I could add new secure/maximum privacy action in the extension UI. Instead of relying on users knowing about the limitations of blur
Security shouldn't be opt-in; you should be secure by default because most users will stay with the default (which is reasonable - the entire point of the extension is to prevent information leaks, and as the author you're the domain expert and your users should be able to trust your judgement which comes in the form of a default).
Also, may I propose that as replacement text before blurring you use ads targeted at computer graphics researchers. /jk