really out of the loop then, because it was like 5 years ago or so :) Firefox add a button to integrate a third party service (pocket) in the default install and i think it added it to your current pinned icon areas (where extension button go). It was also not implemented as a proper extension, so you couldn't actually remove support for it, but only the icon.

Later on Mozilla did buy pocket, so it was no longer third party.

Anyways, a lot of people got super mad with the way they went about it.