User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Firefox/60.0 Build ID: 20100101 Steps to reproduce: I have a multi-monitor setup with a 1920x1080 screen to the left of a 3840x2160 screen with Firefox running on the 2160p screen. When using the mouse wheel to trigger autoscrolling, the autoscroll icon will appear on the 1080p screen outside of the Firefox window (see screenshot) but only when clicking in the leftmost quarter of the Firefox window. I already tracked this issue down to the "layout.css.devPixelsPerPx" setting, which is 1.5 in my case. Using 1.0 solves this issue but makes the UI too small for a 2160p screen. The issue happens independent of the size of the Firefox window as long as it is positioned in the leftmost quarter of the 2160p screen. Steps to reproduce: - Use a multi-monitor setup as described above - Create a new Firefox profile and run Firefox on the right screen - Activate autoscrolling in settings - Set "layout.css.devPixelsPerPx" to 1.5 - Find a scrollable page - Use the mouse wheel to click in the leftmost quarter of the page to trigger autoscrolling Actual results: Autoscroll icon appears on the wrong screen and outside the window. Expected results: Autoscroll icon should appear below the mouse cursor.

Neil, since you patched bug 1457763, if you can, please also have a look at this, possible duplicate of bug 748571, and bug 1444721.

Hey Neil (or timdream), can you please triage this ASAP?

See comment 2

I don't understand this bug enough to do a proper triage. Perhaps Neil could answer?

Probably the same as 1474783.