It's a duplicate of https://support.mozilla.org/ru/questions/970266. Created because of silence and impossibility to change a question's category. The situation descripted is a **problem** one. The question is rather similar to http://support.mozilla.org/ru/questions/962042, but I **do not lock prefs**, so I don't use *mozilla.cfg*. I'm constructing preconfigured Firefox 23.0.1 installation under Win 7 64-bit using browser\defaults\preferences\prefs.js file. Yes, I know that it should be called all-*companyname*.js, but it works in general in my way too. As I have written in subj, when I add to prefs.js file 'pref("privacy.sanitize.sanitizeOnShutdown", true);' line, then lines 'pref("privacy.clearOnShutdown.cookies", true);' and 'pref("privacy.cpd.cookies", true);' stop working. If one run about:config immediately after installation, she would see that the latter two options are switched to false and marked **bold** (changed by user). I had tested it heavily: if one comment out 'pref("privacy.sanitize.sanitizeOnShutdown", true);' line other two preferences work just fine. On the other hand if one add this cursed pref either upper or lower in code - no matter - it would turn both other preferences to *false*. The question is where these strange side-effects are documented? And how can be made a preconfigured installation that possible both sanitize things and clear cookie data on closing? Thanks in advance.