Harden your browser by installing a combination of the following add-ons – these tools extend the privacy and security abilities of Firefox, Chrome, Chromium, and Opera turning them into secure browsing platforms. Note that add-ons built to integrate with Firefox can also added to other browsers based upon Firefox. Online ads may still be using up resources and tracking you, even if the ads are not being displayed. Choose an ad blocker carefully – some ad blockers, such as Ghostery and Adblock Plus will collect user data for profit and/or show you “approved” ads. By far, Firefox offers the most comprehensive set of privacy and security extensions. Here are a few that I use:
HTTPS Everywhere – In spite of some infamous security issues, SSL is still extremely important for keeping your Web traffic safe from prying eyes. If you want to keep nosy packet sniffers out of your business, your Web traffic should always be going through SSL connections. Sadly, not every website supports SSL. Even worse, many websites that do support SSL still default to unencrypted connections -- and the Electronic Frontier Foundation (EFF) wants to change that. The HTTPS Everywhere browser extension, provided for free by the EFF, forces SSL connections on countless websites. Chrome, Firefox, and Opera users can all take advantage of this wonderful extension, and keep important Web traffic private and secure.
Privacy Badger – EFF's Privacy Badger add-on. Available for Chrome, Firefox, and Opera, this browser extension monitors when sites try to track your browsing habits, and automatically thwarts future tracking attempts. The list of blocked content automatically improves as you browse -- no need to manually block trackers. 
Better yet, you can configure this add-on to disable WebRTC tracking as well.
Decentraleyes – A web browser extension that emulates Content Delivery Networks (CDN) to improve your online privacy. It intercepts and blocks incoming traffic from third-party servers, finds supported resources locally, then substitutes and injects them into your browser environment. All of this happens automatically, so no prior configuration is required.
Cookie AutoDelete – Add a tool like Cookie Autodelete that can easily manage and delete pervasive cookies or set your browser to delete all cookies when exiting the browser.
NoScript – This add-on is a JavaScript blocker providing in-depth control over scripts that run on the sites you visit. JavaScript is incredibly powerful, but that useful little scripting language can be used against you. By design, it can deliver detailed information about your system to any Web server. What plug-ins do you have enabled? What size screen are you using? Those small pieces of information can add up, and make tracking your usage profile easier for advertisers and governments. Worse, unpatched JavaScript exploits could potentially be used to trick your browser into giving up even more identifying information. If you want to be truly anonymous, you're going to need to disable JavaScript. That's easier said than done, since many websites rely on JavaScript for core functionality, so you'd be effectively knee-capping your Web browser. But when you use extensions like NoScript, you can manually manage which domains have permission to run JavaScript in your browser. This way, you can whitelist only the domains and webpages that you absolutely trust.
uBlock Origin – A powerful blocker for advertisements and tracking.
uMatrix – While this may be overkill for many users, this powerful add-on gives you control over requests that may be tracking you on various websites. If you use this, you will not need uBlock Origin.
Trace – An advanced extension that can protect many different types of browser fingerprinting such as Canvas/Audio/WebGL Fingerprinting. Trace also offers URL cleaning and header editing features such as the tracking cookie eater and Google header remover.
Disconnect for Facebook – This add-on provides a firewall to prevent Facebook from tracking the webpages you go to by blocking all Facebook related requests sent from all third-party websites, while still allowing you to visit your Facebook account with no problem. It has a very low memory and CPU footprint and can be easily toggled on and off from the toolbar button.
Skip Redirect – Some web pages use intermediary pages before redirecting to a final page. This add-on tries to extract the target URL from the intermediary URL and goes there straight away if successful.
Canvas Blocker – This add-on allows users to prevent websites from using some Javascript APIs to fingerprint them. Users can choose to block the APIs entirely on some or all websites (which may break some websites) or fake its fingerprinting-friendly readout AP.
Decentraleyes – This one protects you against tracking through "free", centralized, content delivery. It prevents a lot of requests from reaching networks like Google Hosted Libraries, and serves local files to keep sites from breaking. Complements regular content blockers. Many web sites are now using third-party CDN (content delivery network) services. CDN providers profit either from direct fees paid by content providers using their network, or profit from the user analytics and tracking data collected as their scripts are being loaded onto customer's websites inside their browser origin. As such these services are being pointed out as potential privacy intrusion for the purpose of behavioral targeting[6] and solutions are being created to restore single-origin serving and caching of resources