Adblock µBlock uBlock Origin : should I have to explain?

Flagfox : Displays a country flag depicting the location of the current website's server and provides quick access to detailed location and webserver information

Greasemonkey Tampermonkey : Allows you to customize the way a webpage displays using small bits of JavaScript (see below for the scripts I use)

Neo Diggler : add a “clear url bar” button, along with some nice shortcuts, similar to Konquefox, but Firefox 6-compatible

User-Agent Switcher : adds a menu and a toolbar button to switch the user agent of the browser

Ghostery Privacy Badger (and Collusion) : because privacy matters

Searchonymous : “Search anonymously on Google, while keeping your search preferences and stay logged in on services such as YouTube, Gmail, etc.”

Wappalyzer : Tells you what software is used on the current visited website

RequestPolicy Continued : Protect from ligatus/outbrain/etc. crap

Channel Blocker YTBlock : remove channels from YouTube video suggestions

SponsorBlock : Same as your favorite ad blocker, but for YouTube videos' sponsored parts

YouTube No Translation : prevents automatic translation on YouTube

AutoAuth : Automatically submits HTTP authentication dialogs when you’ve chosen to have the browser save your login information

Shaarli Shaanti : add a Shaarli button to bookmark delicious links

Two Factor Authenticator : Generates TOTPs for 2 factor authentication (Google Authenticator style)

Dark Reader : “Darth” mode everywhere!

HQTube : automatically selects the HQ version of a Youtube clip

Check Range : allows to check multiple check-boxes at a time, using shift+left click

Disable Youtube Autoplay: because I don't want a fucking jukebox

Disable Youtube next video autoplay: same as above, but for next video (unfortunatly the first one does not seem to work for that)

YT - Overlay remover: hide cards/overlays on youtube videos not working (anymore), use “www.youtube.com##.ytp-ce-element” in uBlock instead

YouTube: Age Verification Bypass: yeah, I'm old enough and I do not want to login

The Ultimate Popup Blocker: hope it will block all these JS silly popups…

Pinterest without registration: allows to browse Pinterest without login/registration, removing the offending modal popup (see below for Facebook)

Facebook and Instagram login popup remover: same as Pinterest but for Facebook & Instagram, obviously.

Instagram Download Button: add the download button and the open button to download or open profile picture and media in the posts, stories, and highlights in Instagram

Manually sort folders : sort account folders

Firetray : display number of unread messages in the tray bar

Lightning : Calendar for Thunderbird

Provider for Google Calendar : sync Google Calendar with Lightning

Exchange 2007/2010 Calendar and Tasks Provider : the perfect companion of Lightning, for those living and working under MS Exchange oppression.

Google Contacts : adds Google Contacts address book

Mailbox Alert : customizable notifications

Smiley Fixer : “Fixes Wingding Smileys in Outlook-generated emails”

SOGo Connector : easy way to do [Cal|Card]dav in Thunderbird

CatchAll Bird : handles incoming messages addressed to all prefix@domain.tld for a fixed domain. for each prefix the AddOn can create a new identity and folder.

Markdown Here Revival : lets you write emails in Markdown and render them as HTML before sending.