Mozilla Firefox became a popular alternative to Microsoft Internet Explorer 6.0 when users sought a browser that could better protect them from spyware and malicious websites. As of 2017, it is the fourth-most popular browser after Google Chrome, Apple Safari, and UC Browser.
On November 14, 2017, Mozilla announced Firefox Quantum, a new technology base for the Firefox browser. Every new version of Firefox for desktop computers use Firefox Quantum technology, beginning with version 57. Mobile versions use the new appearance features (codenamed "Photoni UI"), but not the underlying technology.
Firefox Quantum is roughly twice as fast as previous versions of Firefox, and uses less RAM when browsing. Large portions of Firefox Quantum were re-written using Mozilla's home-grown system programming language, Rust, which provides enhanced thread safety. As a result, Firefox takes greater advantage of multiprocessing capabilities on the user's computer.