Mozilla Firefox is one of the top 3 most popular browsers used by users all over the world. Mozilla is among the organizations that have influenced the WWW in the past two decades in the direction of open and accessible web. Their most popular product is the web browser Firefox, the browser which broke the dominance of Internet Explorer about 10 years ago. Firefox's user base might have declined in the last few years with Google Chrome taking the top spot, however, it still is a safe option to browsing the WWW while being of the the fastest and least resource hungry web browsers.
During the recent Facebook and CA revelations of leaking data of users, I went over my own browser settings to verify that the options were set as to keep me safe and let our minimum amount of user data. For those who want to keep their own data safe while browsing using Firefox, the best is to disable data collection done by Firefox by going to Preferences > Privacy & Security > Firefox Data Collection & Use - and uncheck the two options as shown below:
PS: default settings from Firefox 59.0.2 on LMDE 2, with default options similar in Windows and MacOS builds.