Context: https://bugzilla.mozilla.org/show_bug.cgi?id=984012 (developers discussion on whether to remove it or not). It appears to be an option solely designed for testing purpose, but has been used by some exploits after it escalated privileges (which shouldn't matter, since the exploit already succeeded and there are a thousand ways to do the same), too.
You can find it being used in many places across mozilla source code. https://github.com/search?q=org%3Amozilla+turn_off_all_secur...
You can also find a number of tickets asking for it to be removed, this one is 6 years old :D https://bugzilla.mozilla.org/show_bug.cgi?id=984012