https://developer.mozilla.org/en-US/docs/Mozilla/Command_Line_Options
$ firefox --ProfileManager
or open Firefox and access about:profiles
$ firefox -CreateProfile profile_name profile_dir
$ firefox -CreateProfile JoelUser c:\internet\joelusers-moz-profile
$ firefox -CreateProfile jsEnabled ~/.mozilla/firefox/jsenabled.profile
$ firefox -CreateProfile jsDisabled ~/.mozilla/firefox/jsdisabled.profile
$ firefox --new-instance -P jsEnabled
$ firefox --new-instance -P jsDisabled
$ firefox -P jsEnabled
$ firefox -P jsDisabled
$ firefox -private
$ firefox --private-window
javascript.enabled false
keyword.enabled false
browser.fixup.alternate.enabled false
browser.urlbar.oneOffSearches false
browser.urlbar.update1 false
extensions.pocket.enabled false
Type "about:config” in the address bar
To disable RTCPeerConnection and protect IP addresses leakage, go to about:config and toggle media.peerconnection.enabled to false.
To disable Media Devices, toggle media.navigator.enabled as well as media.peerconnection.enabled both to false.
In preferences, go to General > 'Network Settings' > Settings
Check 'Enable DNS over HTTPS'
Add 'https://dns.quad9.net/dns-query'
$ mkdir -p ~/src
$ cd ~/src
$ git clone https://github.com/arkenfox/user.js.git
$ cp ~/src/user.js/user.js ~/.mozilla/firefox/[profile_directory].default/
$ while read SITE; do firefox-esr "$SITE"; done < ~/sites.txt