Why is that a problem? I never got the furore over it. When it appeared, I removed the icon and just went about my business.
Annoying yes, but certainly not "shady". From what I understood / stand it was a mozilla app they included with the browser, not that different to how firefox comes with a bookmarks app.
Yes, if you're familiar enough with Firefox that you know where to click and are comfortable enough to experiment with customizing your browser. I don't think that's the case for most people.
It took me a few months before I realized that the page was customizable at all, especially since the triple-dot menu doesn't even show up until you hover or focus the element.
I'm a long-time Firefox user, FWIW.