Add-ons

I recommand to install these add-ons.

• uBlock Origin, an advertising and trackers blocker
• HTTPS everywhere, to force encrypted connections
• Decentraleyes, load cloud library from local files
• Cookie Autodelete, advanced cookie management tool

More lists for uBlock Origin

• Anti-trackers list from Disconnect
• Anti-malware list from Disconnect

Search engines

Change the default search engine is a good beginning to protect one’s privacy.
Keep in mind that Firefox is your first search engine. To avoid useless searches, use the history and bookmarks in first place.

Add or remove a search engine in Firefox

• Qwant , French-German, French servers, partial own index, results from Microsoft Bing
• Écosia , Bing’s proxy [1]
• LILO , meta search engine, using Google, Bing and Yahoo [1]
• Startpage, company based in Netherlands, anonymous proxy for Google, acquired by System1, specialized in identification of web users
• Duckduckgo, DNS hosted by Amazon, under PatriotAct, results from Microsoft Bing [1]

Increase the level of privacy in Firefox

• Multi-Account Containers, isolate websites in closed containers
• Containerise (Open websites in containers with automatics rules)
• User Agent Switcher, change the UA [1] to visit websites that block some browsers)
• Privacy Settings, easily access to privacy settings in Firefox
• ClearURLs, clean URL with trackers code (untested)
• CSS Exfil Protection, disable tracking with CSS [2] (untested)
• Don’t touch my tabs, Prevent tabs opened by a hyperlink from hijacking the previous tab (untested)

Redundant add-ons

• Disconnect (useless if uBlockO is configured)
• Privacy Badger (useless if uBlockO is configured)
• Noscript (uBlockO can do the same job)

Add-ons to ban

• Adblock Plus (adblocker) [to ban]
• Ghostery (tracker blocker) [to ban]
• Web Of Trust (websites evaluation collaborative tool) [to ban]

You have now a minimum of privacy with Firefox. Of course I recommend to read more tutorials about privacy. To go further you can also use Firefox profiles.