More info from mozilla.org;
How tracking works
Tracking relies on invisible code embedded in web pages. This code records your visits to websites and collects data about how you interact with pages. When the same tracker appears across multiple websites, it can compile a detailed profile of what you do online. Tracking companies also package, share, and sell this data to users of their service or other third parties.
These tracking techniques occur independent of the browser you use. The following trackers are blocked by default in Firefox, using a list of known trackers provided by Disconnect.
Social media trackers
Social networks place trackers on other websites to follow what you do, see, and watch online. This allows social media companies to collect data about your browsing history and improve their ad targeting. Even if you don’t use a social network, that site can still collect data about your browsing habits.
Social media trackers Firefox blocks and doesn’t block
Firefox blocks the most common trackers from Facebook, Twitter, and LinkedIn that appear on other websites.
The default setting is balanced for protection and performance. Pages will still load normally.
Strict blocks more trackers, but may cause some sites to break. Go to your global privacy preferences to set your Enhanced Tracking Protection settings to Strict.
Social media companies will still be able to collect data about you on their own social networks, including Facebook-owned services like Instagram, WhatsApp, and Messenger. Logging in to sites using your Facebook or Twitter account is another way social networks can collect data about you.
Want even more protection against Facebook? Facebook like and share buttons on other websites allow Facebook to track your browsing activity, even if you never click them. To strip these buttons of Facebook trackers, add the Facebook Container extension.
Cross-site tracking cookies
Cross-site tracking cookies follow you from site to site to gather data about what you do online. This is most often done without your knowledge or consent. Data firms and analytics companies use these cookies to track you, profile you, make inferences about your interests, and retarget you with ads. Because these cookies are set by a different company than the website you’re on, they’re also referred to as third-party tracking cookies.
Cookies Firefox blocks and doesn’t block
By default, Firefox blocks the cookies that track your browsing activity across multiple websites. This includes cross-site tracking cookies set by ad, social media, and analytics companies. Other cookies, such as those that remember your login credentials or items in your shopping cart, are still permitted by default.