Yes, you're right. A better granularity on the permission settings would be a nice feature to add in the webstore. Just to comment on this point, "Your tabs and browsing activity" comes from the fact that the extension modifies the style and UI of Gmail within your browser and so needs to know whether Gmail is open in your browser (i.e. tabs) to apply those changes, nothing more. To make things clear, Gmelius will never access, read, store, or transmit your personal data.