What is Firefox
Firefox is a web browser just like Chrome, Safari and Edge. But unlike Chrome, Safari and Edge, development of Firefox is funded by a non-profit organization called Mozilla. Firefox is an open source project. It means that the source code of the browser is open for inspection by everybody and it is developed by volunteers from around the world. Also, you can install it and use it for free.
Why use Firefox
Firefox is open source which means there's no way a backdoor or some malware can be added to it. Since Firefox and Mozilla are not mired by commercial interests (they don't have to make money because they are a non-profit), we can be sure that they won't sell out their users. Firefox also has pretty good tracking protection turned on by default and it can be made even stronger. Firefox has some neat extensions to protect your online privacy even further. I have listed some of those extensions below. What's more, unlike Chrome, Firefox allows extensions to be installed on Firefox for Android. So, you will get the same protection on both computer and phone.
Install Firefox
Download Fireforx from the official Firefox download page and install it. If you're using F-Droid, click here to install Fennec F-Droid.
Make Firefox even better
Turn on HTTPS-Only mode
Go to Preferences -> Privacy & Security -> HTTPS-Only Mode and select Enable HTTPS-Only Mode in all windows. HTTP connections are plaintext and can be snooped upon easily whereas HTTPS connections are end-to-end encrypted between your device and the server making them much stronger against spying attempts. HTTPS-Only mode won't let you visit plaintext HTTP pages anymore. There is no reason not to use HTTPS for important websites in 2020 anyway.
Enable DNS over HTTPS
Go to Preferences -> General -> Network Settings and enable DNS over HTTPS. This encrypts your DNS requests and prevents your ISP from snooping on your DNS traffic. Currently you can choose between Cloudflare and NextDNS. Both are fine. More providers are likely to be added in the future. You can also use a custom provider like Foundation for Applied Privacy. Or, if you have technical knowledge, you may use Pi-hole and DNSCrypt-proxy through WireGuard tunnel to make your DNS queries private.
Choose a privacy-centric search engine
Go to Preferences -> Search -> Default Search Engine and change the default search engine to Duckduckgo or Qwant. Unlike Google and Bing, Duckduckgo and Qwant don't track you across the internet. An even better option (but harder to set up) will be a self-hosted Searx instance but that's a blog post for another time. Update : I wrote that blog post; you can read how to host a private Searx instance accessible through WireGuard VPN to know more.
Enable Strict Enhanced Tracking Protection
Go to Preferences -> Privacy & Security -> Browser Privacy and in Enhanced Tracking Protection, choose Strict protection to block tracking content in all windows.
Excellent Extensions
I have listed some must-have extensions below that can help protect your online privacy. All these extensions are part of the Recommended Extensions program run by Mozilla. And they are all open source and they meet high standards of security and performance required by Mozilla.
uBlock Origin
It's the most effective content blocker around. It blocks ads, tracking scripts, tracking cookies, malware serving sites and much more. It's also very lightweight. By preventing the browser from downloading and executing tracking scripts, you actually save some bandwidth and CPU cycles and as a result webpages load faster than usual and you save some battery power too. Get uBlock Origin for Firefox.
HTTPS Everywhere
If you have enabled HTTPS-Only Mode in Preferences, you can skip this extension. HTTPS Everywhere automatically redirects visitors from HTTP website to HTTPS version of the same website, if it is available. Get HTTPS Everywhere for Firefox.
Privacy Badger
Privacy Badger blocks third-party trackers from following you around the web. It automatically learns what unknown third-party trackers do as you browse the web and if they track you, Privacy Badger blocks them. Get Privacy Badger for Firefox.
Decentraleyes
Decentraleyes prevents tracking done by content delivery networks or CDNs. As you browse the web, lots of third party Javascript and CSS files are downloaded from the same few companies which offer CDN facility. Those companies then know which websites you visited. Decentraleyes has a local copy of many common Javascript and CSS files so you don't have to connect to those pesky CDNs as often. Get Decentraleyes for Firefox.
ClearURLs
ClearURLs blocks tracking done through URLs. You may have seen long and unweildy URLs which have querystrings like ?ref=long-uniqid or &utm_source=long-uniq-id. These portions of the URL tell the server where you were before and from where you got the link among other things. ClearURLs removes these parts of the URL. ClearURLs also blocks tracking done through eTags. Get ClearURLs for Firefox.
Firefox Multi-Account Containers
It's an extension by Firefox developers themselves. It offers separation between various aspects of your online activity. For example, if you log into an e-commerce website in 'Shopping' container tab, the website won't track you outside 'Shopping' tabs. Also, if you log into your email provider in 'Work' tab, but you have a personal account with the same email provider, just open a 'Personal' tab and you can log in to your other account at the same time. Cookies are separated by container types allowing you to do this. Get Firefox Multi-Account Containers.