The articles on this whole controversy describe it as an ARG - an Alternate Reality Game. I don't know exactly how this ARG works, but ARGs in general are like

The articles on this whole controversy describe it as an ARG - an Alternate Reality Game. I don't know exactly how this ARG works, but ARGs in general are like scavenger hunts - players investigate what's causing the changes, which give them hints as to where to look next. So presumably it was implemented as a browser extension so game players would be able to find the browser extension, which would give them hints about what to do next.