Maximize/"Harden" Firefox privacy settings
(via Mental Outlaw YT channel and Chris Xiao's Yet Another Firefox Hardening
article and Unix Sheikh's Choose your Browser Carefully article):

Install Ublock Origin
Install Decentraleyes
Install Always active Window - Always Visible
Install Canvas Blocker (on librewolf no need)
Install Classic mode for Wikipedia
Install Colorzilla
Install Cookie AutoDelete
Install Measure-it
Install FastForward
Install Firefox Translations
Install Github Gloc (reads lines of code on github repos, requires personal access token)
Install LocalCDN (conflicts witht Decentraleyes)
Install FastForward
Install NoScript
Install Chameleon
Install User-Agent-Switcher and Manager
Install OverbiteWX
Install OneTab (set OneTab to not open up on startup)
Install Return YouTube Dislike
Install Alter (redirect for nitter, invidious, teddit, scribe, bibliogram, etc.)
Install bypass-paywalls (not official, go to https://github.com/iamadamdev/bypass-paywalls-chrome)
Install DuckDuckGo Lite Search (Librewolf has this by default)
Install Stack Overflow Prettifier
Install SponsorBlock for Youtube-Skip Sponsorships (under Misc, enable invidious 3rd party)
Install ClearURLs
Install Always active Window
Install DarkReader (in DarkReader menu under More, set to Static)
Install Vimium-FF
Insall Vue.js devtools
Install WAVE Evaluation Tool
Install Manjaro Theme (matcha-dark-azul for blue, matcha-dark-sea for green)
Set Default Search Engine to Duck Duck Go Lite
Get Firefox to remember nothing through Preferences setting
Set Firefox to never visit non  https websites
Disable smooth scrolling

about:config settings
(Optional): Turn off Javascript
media.peerconnection.enabled set to false #breaks real-time audio/video
media.navigator.enabled to false #breaks real-time audio/video
media.gmp
devtools.onboarding.telemetry.logged to false
datareporting.policy.dataSubmissionEnabled set to false
app.normandy.enabled set to false
extensions.pocket.enabled to false
extensions.formautofill.available set to blank
extensions.screenshots.disabled set to true
extensions.webcompat-reporter.enabled set to false
privacy.resistfingerprinting set to true #noticeable performance and stability impact, proceed with caution.
privacy.firstparty.isolate to true
network.dns.disablePrefetch to true
network.predictor.enabled set to false
network.prefetch-next to false
network.http.sendRefererHeader to 0 #sites with forms and logins may break
network.http.referer.XoriginPolicy to 1
network.cookie.lifetimePolicy to 2
pdfjs.enableScripting to false
identity.fxaccounts.enabled to false
geo.enabled to false
dom.webnotifications.enabled to false
security.ssl3.rsa_des_ede3_sha set to false
security.ssl.require_safe_negotiation set to true
security.tls.version set to at least 3 (4 highest setting as of 2021, but not necessary according to Mental Outlaw)
security.tls.enable_Ortt_data set to false
browser.shell.checkDefaultBrowser = false
browser.formfill.enable set to false
browser.cache.disk.enable set to false
browser.cache.disk_cache_ssl set to false
browser.cache.memory.enable set to false
browser.cache.offline.enable set to false
browser.cache.insecure.enable set to false
browser.privatebrowsing.autostart set to true
browser.urlbar.speculativeConnect.enabled set to false
browser.urlbar.maxRichResults set to 0
browser.search.suggest.enabled set to false
plugin.scan.plid.all set to false (same, couldn't find)
browser.ping-centre.telemetry set to false
browser.newtabpage.activity-stream.feeds.telemetry set to false
browser.newtabpage.activity-stream.telemetry set to false
browser.newtabpage.activity-stream.section.highlights.includePocket to false
browser.tabs.crashReporting.sendReport to false
browser.tabs.tabmanager.enabled to false
browser.uidensity to 1 (makes the browser's tabs not so huge for firefox 89+)
browser.chrome.site_icons to false (removes favicons)
browser.tabs.tabsmanager.enabled to false
accessibility.force_disabled to 1 (improves performance)
extensions.unifiedExtensions.enabled to false (to remove item visually, remove all extensions from list)
devtools.onboarding.telemetry.logged to false
toolkit.telemetry.enabled to false
toolkit.telemetry.server Delete the URL and leave it empty
toolkit.telemetry.archive.enabled set to false
toolkit.telemetry.bhrPing.enabled set to false
toolkit.telemetry.firstShutdownPing.enabled set to false
toolkit.telemetry.newProfilePing.enabled set to false
toolkit.telemetry.unified set to false
toolkit.telemetry.updatePing.enabled set to false
toolkit.telemetry.shutdownPingSender.enabled set to false
webgl.disabled set to true
privacy.firstparty.isolate set to true
security.ssl.enable_false_start set to false

go into ublock origin and check the 'Prevent WebRTC from leaking local IP addresses' box.
go into usr/lib/firefox/distribution and open/create package.json and input the following:

{
  "policies": {
    "DisableAppUpdate": true,
    "DisableFirefoxAccounts": true,
    "DisableTelemetry": true,
    "DNSOverHTTPS": {
      "Enabled": false,
      "Locked": true
    },
    "DontCheckDefaultBrowser": true,
    "NetworkPrediction": false,
    "PromptForDownloadLocation": true,
    "SearchEngines": {
      "PreventInstalls": true
    },
    "SearchSuggestEnabled": false,
    "NetworkPrediction": false
  }
}

The following isn't privacy related, but turns off proton in firefox, which makes better use of screenspace:

browser.proton.enabled set to false
browser.proton.modals.enabled set to false
browser.proton.doorhangers.enabled set to false
browser.proton.contextmenus.enabled set to false
browser.sessionstore.resum_from_crash false

Copy the chrome directory into the profile ($HOME/.librewolf/*.default-release)
This feature isn't officially supported anymore so enable it by heading to
about:config and find/set:
toolkit.legacyUserProfileCustomizations.stylesheets : true

Custom Caret Widths for Text Cursor:
In about:config, add these new custom properties (they don't exist by default):
ui.caretWidth (set to number, and set to 10)
ui.caretBlinkTime (set to number, and set to 0 to disable blink)

Go into Ublock Origin, Under Filter List, open Annoyances and click all
checkboxes (blocks annoying cookie confirmation popups amongst others).

Disable JavaScript JIT Compiler:
javascript.options.baselinejit false
javascript.options.ion false
javascript.options.wasm false
javascript.options.asmjs false

In about:preferences#privacy:

Enable secure DNS using Default protection.
Use custom secure DNS, under Max Protection, input mullvad's DNS server:
https://base.dns.mullvad.net/dns-query