As originally defined, an OS is a set of functionalities offered to user-programs for accessing hardware, memory and similar things at a higher level - in it's original intent, an OS was passive. A browser originally also had the intent of being just a receiver/displayer of the information the user requested. Of course, browsers have indeed become more likes OSes as web pages have become like programs.

Of course, mobile OSes and OSes in general have become active and oriented to filtering input as well as generating inputs. This creep is everywhere - MS Windows displaying adds and flogging it's "app store" is one notably noxious example.