Change Firefox's zoom by script
Each time I change the monitor I have to zoom in or out firefox. Here’s how to set it via script:

Figure 1: Large
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Figure 2: Small
Locate the appropriate file
ls /home/*/.mozilla/firefox/*/prefs.js
Locate the appropriate parameter
grep layout.css.devPixelsPerPx /home/*/.mozilla/firefox/*/prefs.js
Large screen: Set the zoom
#!/usr/bin/env bash
factor=2.5
if grep 'layout.css.devPixelsPerPx' /home/*/.mozilla/firefox/*/prefs.js
then
sed -i -e "s/^user_pref(\"layout.css.devPixelsPerPx.*$/user_pref(\"layout.css.devPixelsPerPx\", \"$factor\");/" /home/*/.mozilla/firefox/*/prefs.js
else
echo "user_pref(\"layout.css.devPixelsPerPx\", \"$factor\");" >> /home/*/.mozilla/firefox/*/prefs.js
fi
Small screen: Set the zoom
#!/usr/bin/env bash
factor=1.0
if grep 'layout.css.devPixelsPerPx' /home/*/.mozilla/firefox/*/prefs.js
then
sed -i -e "s/^user_pref(\"layout.css.devPixelsPerPx.*$/user_pref(\"layout.css.devPixelsPerPx\", \"$factor\");/" /home/*/.mozilla/firefox/*/prefs.js
else
echo "user_pref(\"layout.css.devPixelsPerPx\", \"$factor\");" >> /home/*/.mozilla/firefox/*/prefs.js
fi
Make the scripts executable
sudo chmod --verbose +x ~/src/scripts/FirefoxZoomIn.sh
sudo chmod --verbose +x ~/src/scripts/FirefoxZoomOut.sh
~/src/scripts/FirefoxZoomIn.sh
~/src/scripts/FirefoxZoomOut.sh
Docking/undocking triggers those scripts, which I’m handling with Autorandr.