User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:52.0) Gecko/20100101 Firefox/52.0 Build ID: 20170303012758 Steps to reproduce: Open a story on slashdot.org (e.g., https://science.slashdot.org/story/17/03/10/1414202/nasa-finds-lunar-spacecraft-that-vanished-8-years-ago) in incognito mode, so you get the default desktop site. Between the summary and the top comment there is a bar containing a slider with two handles, controlling the number of displayed comments. Under Win 8.1, on a touchscreen device, running FF 51.0.1, it's possible to gently tap a slider and immediately drag it to the right. Actual results: With FF 52, the tap + drag doesn't work. Expected results: Tap + drag should work like click + drag with the mouse. It's not the only touch UI difference between 51 and 52, but it's the most annoying.
In 52 we are now sending touch events instead of mouse events, and the page reimplements drag behaviour with mouse events, so it doesn't work with touch events. Same behaviour in Chrome and Edge. They would need to fix their code to deal with touch events.