it's dangerous to browse the internet alone!
here take these!

general

• violentmonkey (official website)
  • functions similarly to extensions
  • scripts for specific sites (e.g. youtube). screenshot of the extension.
• stylus (official website)
  • modify how websites look with only css
  • you can also write your own. screenshot of the extension.
• dark reader (official website)

block ads and trackers

• ublock origin (firefox/chrome)
  • works best on firefox
  • consider ublock origin lite if you are on chromium-based browsers. read the differences here.
• libredirect (official website)
  • redirects popular websites to "alternative privacy-friendly frontends"
  • bypasses login walls
  • you still have to log in/register for some services for anything beyond browsing
  • useful tools such as Send, a file sharing website

youtube

• sponsorblock (official website)
• return youtube dislike (official website)