The extension ecosystem is the number one reason many people are still using Firefox. Amid all the "user experience" bullshit, the deprecated-then-removed features, and the asshats steering Mozilla, it was extensions that kept the browser usable.
This was the last vestige of the Firefox that we knew and loved being ripped out and tossed aside. In 2-3 years Firefox will be nothing more than another shitty Chrome clone. I can only hope this absurd move leads to a serious fork of the browser that focuses on getting back to the original goals of Firefox.