[mschulze]

I am using my Dell XPS 13 with a resolution of 1920x1080 (scaled from 3200x1800) for the internal display and an external display with native 1920x1080 and cannot confirm this. It works pretty well (GNOME3, Ubuntu 17.04). Firefox is not tiny. I did not change anything in my X config files.

[majewsky]

You mean you changed the resolution of your internal screen with xrandr? Or does xrandr still report 3200x1800? If not, then this is not a HiDPI setup. HiDPI is (basically) when applications draw using internal coordinates that are not "1 screen pixel per logical pixel", but more than that.

[mschulze]

No, I just changed the "Display settings" (right click on desktop) to 1920x1080.

xrandr reports the following:

Screen 0: minimum 320 x 200, current 3840 x 1080, maximum 8192 x 8192 eDP-1 connected 1920x1080+1920+0 (normal left inverted right x axis y axis) 294mm x 165mm