This webNavigation permission is needed for us in order to be able to set cookie for the wikiwand.com domain when your page is loaded. We need this cookie to let our backend know if the corresponding user has the wikiwand extension or not. Later we will sync functionality of the Firefox extension with the Chrome extension and, for instance, Firefox user will have an ability to Ctrl+Click on terms and give immediate Wikiwand pop-up with term definition. To implement such a thing we need to have an ability to inject our client JS scripts into the pages. Please refer our Chrome web store where you will find more details about further functionality