Awesome Privacy

Blocks invisible trackers, in order to stop advertisers and other third-parties from secretly tracking where you go and what pages you look at. Download: Chrome - Firefox

Allows you to block the execution of certain scripts. Download: Chrome - Opera

Firefox Multi-Account Containers lets you keep parts of your online life separated into color-coded tabs that preserve your privacy. Cookies are separated by container, allowing you to use the web with multiple identities or accounts simultaneously. Download: Firefox

Provides user control over WebRTC privacy settings in Chromium, in order to prevent WebRTC leaks. Download: Chrome. For Firefox users, you can do this through browser settings. Test for WebRTC leaks, with browserleaks.com/webrtc

Block fingerprint without removing access to HTML5 Canvas element. Canvas fingerprinting is commonly used for tracking, this extension helps to mitigate this through disallowing the browser to generate a true unique key Download: Chrome - Firefox - Edge

This extension will automatically remove tracking elements from the GET parameters of URLs to help protect some privacy Download: Chrome - Firefox / Source

Sanitizes and blocks any CSS rules which may be designed to steal data, in order to guard against Exfil attacks Download: Chrome - Firefox - Source

Enables the First Party isolation preference (Clicking the Fishbowl icon temporarily disables it) Download: Firefox

Prevent Firefox from sending Origin headers when they are least likely to be necessary, to protect your privacy Download: Firefox - Source

Emulates remote frameworks (e.g. jQuery, Bootstrap, Angular) and delivers them as local resource. Prevents unnecessary 3rd party requests to tracking CDNs Download: Firefox

Similar to LocalCDN, Serves up local versions of common scripts instead of calling to 3rd-party CDN. Improves privacy and load times. Works out-of-the-box and plays nicely with regular content blockers. Download: Chrome - Firefox - Opera - Pale Moon - Source

Simple extension by DuckDuckGo, which grades the security of each site. Download: Chrome
Firefox

A simple web extension that redirects Twitter, YouTube, Instagram & Google Maps requests to privacy friendly alternatives Download: Firefox - Chrome

Spoofs browser's User-Agent string, making it appear that you are on a different device, browser and version to what you are actually using. This alone does very little for privacy, but combined with other tools, can allow you to keep your fingerprint changing, and feed fake info to sites tracking you. Some websites show different content, depending on your user agent. Download: Chrome - Firefox - Edge - Opera - Source

The companion extension for PrivacySpy.org - an open project that rates, annotates, and archives privacy policies. The extension shows a score for the privacy policy of the current website. Download: Chrome - Firefox

Simplified HTTPS upgrades for Firefox (lightweight alternative to HTTPS-Everywhere) Download: Firefox

Some web pages use intermediary pages before redirecting to a final page. This add-on tries to extract the final url from the intermediary url and goes there straight away if successful Download: Firefox - Source

View archived and cached versions of web pages on 10+ search engines, such as the Wayback Machine, Archive.is, Google etc Useful for checking legitimacy of websites, and viewing change logs Download: Firefox - Chrome - Edge - Source

Displays a country flag depicting the location of the current website's server, which can be useful to know at a glance. Click icon for more tools such as site safety checks, whois, validation etc Download: Firefox

Visualize in detail the servers you are contacting when you are surfing on the Internet. Created by Gary Kovacs (former CEO of Mozilla), presented in his TED Talk. Download: Firefox - Source

Helps protect web searchers from surveillance and data-profiling, through creating meaningless noise and obfuscation, outlined in their whitepaper. Controversial whether or not this is a good approach Download: Firefox - Source

Enables you to better understand the evolution of browser fingerprints (which is what websites use to uniquely identify and track you). Download: Chrome - Firefox

Notifies you when visiting a known or potential phishing site, and detects suspicious JavaScript (including skimmers and miners). Also provides a simple rating for a given site's legitimacy and security. Great for less technical users. Netcraft also has a handy online tool: Site Report for checking what any given website is running. Download: Chrome \ Firefox \ Opera \ Edge

NOTE On modern browsers, this is no longer needed Forces sites to load in HTTPS, in order to encrypt your communications with websites, making your browsing more secure (Similar to Smart HTTPS). Note this functionality is now included by default in most modern browsers. Download: Chrome
Firefox

Linguist is a privacy‑focused translation solution in-browser that has an embedded offline translator and lets users create custom translators to use any translation API, even if it's locally deployed. Full-page translation, selected text translation, dictionary, history, and other features you may expect of a full-featured translation solution in-browser. Download: Chrome / Firefox