Firefox Extensions

Security / Privacy

uBlock Origin
Blocks bad elements and resources, like ads, popups asking to allow ads, tracking, malware links, share links…
NoScript
Choose which domains are allowed to execute JavaScript
uMatrix
Advanced firewall: choose what type of HTTP request is allowed from which domain
Cookie AutoDelete
Automatically deletes cookies from non-whitelisted domains
Smart Referer
Only send referer HTTP header when necessary
DNSSEC/DANE Validator
As the name suggests, performs DNSSEC and DANE validations on the browser; requires a DoH resolver

Information

Indicate TLS
Displays TLS parameters used for the connection with the website.
SixIndicator
Displays IP versions and addresses used for the connection with the website.

Customization

Stylus
Set your own CSS rules, override server-sent CSS
Midnight Lizard
Automatic dark theme creator, with advanced settings
Firefox Color
Choose Firefox interface colors

Specific

SponsorBlock
Skips sponsored and annoying content from YouTube videos
Privacy Redirect
Redirects to alternative front-ends: YouTube → Invidious…