True DPI settings in X

etc X11 xinit xinitrc.d 01-dpi.sh

# change this to whatever you need
export DPI=165

# hardly useful
xrandr --dpi $DPI

# used by a couple of legacy applications
echo 'Xft.dpi: '$DPI | xrdb -merge -

# the point here is to increase the mouse cursor size - adjust to your preference
echo 'Xcursor.size: 32' | xrdb -merge -

# select a larger default font for old X applications or terminals like urxvt
echo '*font: -*-helvetica-medium-r-*-*-*-140-*-*-*-*-iso10646-*' | xrdb -merge -

# this is probably the most important setting, most applications read the DPI from xsettings
echo Xft/DPI $((DPI*1024)) >> ~/.xsettingsd
xsettingsd & # or pkill -HUP xsettingsd if it is already running

usr lib firefox defaults pref local-settings.js

pref("general.config.obscure_value", 0); // only needed if you do not want to obscure the content with ROT-13
pref("general.config.filename", "mozilla.cfg");

usr lib firefox mozilla.cfg

//
defaultPref('layout.css.devPixelsPerPx', ''+(Math.floor(parseFloat(getenv('DPI'))/9.6)/10));
lockPref('layout.css.devPixelsPerPx', ''+(Math.floor(parseFloat(getenv('DPI'))/9.6)/10));