Preparation:

    Enter "about:config" in the Firefox address bar and press enter.
    Press the button "Accept the Risk and Continue" [FF71+] or "I accept the risk".
    Copy and paste each of the preferences below (for example "webgl.disabled") into the search bar, and set each of them to the stated value (such as "true").

Getting started:

privacy.firstparty.isolate = true
    A result of the Tor Uplift effort, this preference isolates all browser identifier sources (e.g. cookies) to the first party domain, with the goal of preventing tracking across different domains. (Don't do this if you are using the Firefox Addon "Cookie AutoDelete" with Firefox v58 or below.)
	
privacy.resistFingerprinting = true
    A result of the Tor Uplift effort, this preference makes Firefox more resistant to browser fingerprinting.

privacy.trackingprotection.fingerprinting.enabled = true
    [FF67+] Blocks Fingerprinting

privacy.trackingprotection.cryptomining.enabled = true
    [FF67+] Blocks CryptoMining

privacy.trackingprotection.enabled = true
    This is Mozilla's new built-in tracking protection. One of it's benefits is blocking tracking (i.e. Google Analytics) on privileged pages where add-ons that usually do that are disabled.

browser.send_pings = false
    The attribute would be useful for letting websites track visitors' clicks.

browser.urlbar.speculativeConnect.enabled = false
    Disable preloading of autocomplete URLs. Firefox preloads URLs that autocomplete when a user types into the address bar, which is a concern if URLs are suggested that the user does not want to connect to.

dom.event.clipboardevents.enabled = false
    Disable that websites can get notifications if you copy, paste, or cut something from a web page, and it lets them know which part of the page had been selected.

media.eme.enabled = false

    Disables playback of DRM-controlled HTML5 content, which, if enabled, automatically downloads the Widevine Content Decryption Module provided by Google Inc. 

    DRM-controlled content that requires the Adobe Flash or Microsoft Silverlight NPAPI plugins will still play, if installed and enabled in Firefox.

media.gmp-widevinecdm.enabled = false
    Disables the Widevine Content Decryption Module provided by Google Inc., used for the playback of DRM-controlled HTML5 content.

media.navigator.enabled = false
    Websites can track the microphone and camera status of your device.

network.cookie.cookieBehavior = 1
    Disable cookies

        0 = Accept all cookies by default
        1 = Only accept from the originating site (block third-party cookies)
        2 = Block all cookies by default

network.http.referer.XOriginPolicy = 2
    Only send Referer header when the full hostnames match. (Note: if you notice significant breakage, you might try 1 combined with an XOriginTrimmingPolicy tweak below.)

        0 = Send Referer in all cases
        1 = Send Referer to same eTLD sites
        2 = Send Referer only when the full hostnames match

network.http.referer.XOriginTrimmingPolicy = 2
    When sending Referer across origins, only send scheme, host, and port in the Referer header of cross-origin requests.

        0 = Send full url in Referer
        1 = Send url without query string in Referer
        2 = Only send scheme, host, and port in Referer

webgl.disabled = true
    WebGL is a potential security risk.

browser.sessionstore.privacy_level = 2
    This preference controls when to store extra information about a session: contents of forms, scrollbar positions, cookies, and POST data.

        0 = Store extra session data for any site. (Default starting with Firefox 4.)
        1 = Store extra session data for unencrypted (non-HTTPS) sites only. (Default before Firefox 4.)
        2 = Never store extra session data.

beacon.enabled = false
    Disables sending additional analytics to web servers.

browser.safebrowsing.downloads.remote.enabled = false
    Prevents Firefox from sending information about downloaded executable files to Google Safe Browsing to determine whether it should be blocked for safety reasons.

Disable Firefox prefetching pages it thinks you will visit next:
    Prefetching causes cookies from the prefetched site to be loaded and other potentially unwanted behavior. 

        network.dns.disablePrefetch = true
        network.dns.disablePrefetchFromHTTPS = true
        network.predictor.enabled = false
        network.predictor.enable-prefetch = false
        network.prefetch-next = false

network.IDN_show_punycode = true
    Not rendering IDNs as their Punycode equivalent leaves you open to phishing attacks that can be very difficult to notice.