Welcome to the forum! 
There’s no point in that. GNU/Linux is a multiuser operating system, and there is a distinction between system data and user data. Firefox’ user data is stored in the user’s home directory, and uninstalling or reinstalling the application does not affect the data in your home directory.
You need to allow cookies. Even this forum uses them. Among other things, it allows websites to log you in and keep you logged in for as long as you want.
These three must be blocked, of course.
Just set the built-in protection in Firefox to “Standard” and install DuckDuckGo Privacy Essentials. You can do that just for your user account by visiting DuckDuckGo — you’ll immediately get a link for installing it in your browser — or you can install it systemwide from the AUR. 
pamac build firefox-extension-duckduckgo-privacy-essentials