Is possible to include these two things in the user.js?

[kalkulusrampage]

Going through the 'optional hardening' section found this:

Sanitize on close

Clear browsing data on shutdown:

Go to ☰ → Settings → Privacy & Security → Cookies and Site Data → Delete cookies and site data when Firefox is closed

You can allow exceptions if you want to stay logged in to some sites:

Go to ☰ → Settings → Privacy & Security → Cookies and Site Data → Manage Exceptions
For cross-domain logins, add exceptions for both sites
    e.g. https://www.youtube.com (site) + https://accounts.google.com (single sign on)

Wondering if these two things, "Delete cookies and site data when Firefox is closed" and the list of exception domains can be done via user.js file instead of manually.

[yokoffing]

Delete cookies and site data when Firefox is closed

It used to be user_pref("network.cookie.lifetimePolicy", 2);, but that was removed.

Currently, toggling on that setting in the UI flips the following prefs to true:

privacy.sanitize.sanitizeOnShutdown
privacy.clearOnShutdown.cache
privacy.clearOnShutdown.cookies
privacy.clearOnShutdown.offlineApps

But if you want everything cleared (minus site exceptions if you use them), then you'll need:

// PREF: clear browsing data on shutdown
user_pref("privacy.sanitize.sanitizeOnShutdown", true);
user_pref("privacy.clearOnShutdown.history", true);
user_pref("privacy.clearOnShutdown.formdata", true);
user_pref("privacy.clearOnShutdown.sessions", true);
user_pref("privacy.clearOnShutdown.cache", true);
user_pref("privacy.clearOnShutdown.cookies", true);
user_pref("privacy.clearOnShutdown.offlineApps", true);
user_pref("privacy.clearOnShutdown.siteSettings", false); // enforce
user_pref("browser.sessionstore.privacy_level", 2);

If you have session restore enable (Settings → General → Startup → Opened previous windows and tabs), then you will need to omit privacy.clearOnShutdown.history for session restore to work.

list of exception domains can be done via user.js

Betterfox/Securefox.js

Lines 467 to 470 in 0334bea

	// PREF: configure site exceptions
	// [NOTE] Currently, there is no way to add sites via about:config
	// [SETTING] to manage site exceptions: Options>Privacy & Security>Cookies & Site Data>Manage Exceptions
	// or when on the website in question: Ctrl+I>Permissions>Cookies>Allow

[kalkulusrampage]

Thanks man, that works perfectly, I definitely will go through all the files to learn more about Firefox and the fantastic work you are doing here. Totally a fan.

[kalkulusrampage]

About this:

For cross-domain logins, add exceptions for both sites:
// e.g. https://www.youtube.com (site) + https://accounts.google.com (single sign on)

I just logged on youtube and just allow as exception accounts.google, after that and clearing all except site.Setting and history, youtube and all google related webs login automatically just with accounts.google as exception (no need to add the site too)

[yokoffing]

login automatically just with accounts.google as exception (no need to add the site too)

I have observed this behavior myself for a long time, but I've kept it in the documentation for now. It doesn't hurt either way, but there may be some nuanced difference I've overlooked.