When ever I am trying to look for some image or search some thing and when I scroll down a black bar appear on the lower side of my browser at first I thought its just log but over the time I think its some kind of bugs, because I try both of the page I visit on firefox, firefox beta, and firefox nightly, beta & nightly dont seems to be a problem to some of the page I visited its must be the official firefox apps... even tho I still love firefox its one of the browser i feel I am free to use and a browser that I choice not force to use, so mozilla keep up the good work hope you able to fix some bugs fast 😁😁