Browser Plugins

All these browser plugins work in Firefox, some also in Chrome/Chromium

Beginners

HTTPS Everywhere: Enables HTTPS by default on many websites,
straightforward and very easy to use (you basically forget about it)
Also available for Chrome, Firefox for Android & Opera.
More info about HTTPS Everywhere & Tor here

Ublock Origin: Blocks a huge amount of ads, same, you just forget
about it and never want to use a browser without it again.
It is available for Firefox, Chrome, Safari

Privacy Badger: Also available for Chrome

Terms of Service; Didn’t Read: a user rights initiative to rate and label website terms & privacy policies, from very good Class A to very bad Class E. Add-on/extension for Firefox, Chrome, Safari & Opera with Internet Explorer to come

 

Intermediate

Lightbeam: a Firefox add-on that uses interactive visualizations to show you the first and third party sites you interact with on the Web. As you browse, Lightbeam reveals the full depth of the Web today, including parts that are not transparent to the average user.

Advanced

NoScript: Blocks javascripts by default, breaks most of the web2.0
websites, the user needs to know what they are doing.

 

Tor Browser Launcher

To install in an Ubuntu-based distribution
https://github.com/micahflee/torbrowser-launcher

 

Obfuscation

TrackMeNot: a lightweight browser extension that helps protect web searchers from surveillance and data-profiling by search engines

AdNauseam:  a browser extension designed to obfuscate browsing data and protect users from surveillance and tracking by advertising networks.