This bug applies also to Firefox-esr in Stretch: The only difference is the directory name, here affected files are:
/usr/share/firefox-esr/browser/defaults/preferences/webide-prefs.js /usr/share/firefox-esr/browser/defaults/preferences/firefox.js /usr/share/firefox-esr/browser/defaults/preferences/devtools.js All 3 files have a modification date of 2010, January 1st, which did not change since Firefox 45 was introduced in Stretch.
