Just the title of this post alone should make it more than obvious that the article is not about preventing anyone to view data, but rather to grant anyone access to it in an exploitative way.

In response to the article itself: you might even be able to get such an extension on the Firefox Extensions store and just maybe get a "Recommended" status too. Refer to my comment in another post from a few days ago for other such current violations: https://news.ycombinator.com/item?id=34832280