Mozilla Firefox is a great web browser that offers a great number of various features and customization options and it is designed to be a fast and secure web browser. The newest version of Mozilla Firefox is called Firefox Quantum and it is a version number 60. Mozilla Firefox is one of the most popular open-source web browsers which was known as Phoenix at first and it was a browser that contained features like download manager or tabbed browsing when these features were not present in other browsers. Mozilla Firefox Is Using Way To Much Memory.