Firefox has been offering a "Do Not Track" option for quite a while (under Tools / Options / Privacy ). The problem is that websites were not required to honor that request.
Firefox has now added an new feature, called "Tracking PROTECTION", which uses a blocklist to actively block domains and sites that are known to track users.
For details --- including how to activate this feature --- see https://finance.yahoo.com/news/firefox-helps-cover-assets-latest-174857917.html
Firefox’s optional Tracking Protection reduces load time for top news sites by 44%
A duo of former Mozilla software engineers "found that with Tracking Protection enabled, the Alexa top 200 news sites saw a 67.5 percent reduction in the number of HTTP cookies set. Furthermore, performance benefits included a 44 percent median reduction in page load time and 39 percent reduction in data usage".
