The setup of my Dell XPS 13 laptop with Ubuntu.
July 2016
My screen resolution is 1920x1080 for a 13.3″ screen. Thus I needed to increase the pixel density, else everything would be too small. I followed the advices on adapt-ubuntu-to-a-high-dpi-resolution-screen. I entered 1.38 for the system wide "Scale for menu and title bars" value. I entered 1.4 for the layout.css.devPixelsPerPx value in about:config for Firefox / Thunderbird. The case of the Atom editor was trickier. I ended up using the following option:
atom --force-device-scale-factor=1