I mentioned this problem with my own extension. It’s not my extension. I tried loading Adblock Plus and get the same non-functional slider.
I have no other extensions loaded other than the H264 codec that Mozilla ships pre-installed.
Add-on installs fine if I request the desktop site and touch the install button there. It’s just the slider widget that’s broken.
Firefox 54.0.1, Android 4.1.2. Cat B15 phone.