# This affects every GTK app.
xfconf-query -c xsettings -p /Xft/DPI -s 144
The second step is going to about:config in Firefox, and setting layout.css.devPixelsPerPx to a higher value than 1.0. I really need to write an extension to do that in one click.What is really tricky, though, it's having two monitors with different DPI. Win 10 does an acceptable job with it; no Linux tools I'm aware of can handle it reasonably well. Some xrandr incantations can offer partial solutions.