Firefox has both the option of granting the permission only for the current pageload (this is in fact the default behavior!) and exactly the "click the icon and

Firefox has both the option of granting the permission only for the current pageload (this is in fact the default behavior!) and exactly the "click the icon and revoke the permission" behavior you are asking for once you have granted the permission. So "browsers" already do this, for some values of "browsers". l) [Disclaimer: I work on Firefox.]