The project began as an experimental branch of the Mozilla project by Dave Hyatt, Joe Hewitt, and Blake Ross. They believed the commercial requirements of Netscape's sponsorship and developer-driven feature creep compromised the utility of the Mozilla browser. To combat what they saw as the Mozilla Suite's software bloat, they created a stand-alone browser, with which they intended to replace the Mozilla Suite. On April 3, 2003, the Mozilla Organization announced that they planned to change their focus from the Mozilla Suite to Firefox and Thunderbird. The community-driven SeaMonkey was formed and eventually replaced the Mozilla Application Suite in 2005.
The Firefox project has undergone several name changes. It was originally titled Phoenix, which carried the implication of the mythical firebird that rose triumphantly from the ashes of its dead predecessor, in this case from the "ashes" of Netscape Navigator after it had been killed off by Microsoft Internet Explorer in the "First Browser War". Phoenix was renamed due to trademark issues with Phoenix Technologies; the replacement name, Firebird, provoked an intense response from the Firebird database software project. In response, the Mozilla Foundation stated that the browser would always bear the name Mozilla Firebird to avoid confusion. After further pressure, on February 9, 2004, Mozilla Firebird became Mozilla Firefox. The name Firefox was said to be derived from a nickname of the red panda, which became the mascot for the newly named project. For the abbreviation of Firefox, Mozilla prefers Fx or fx, though it is often abbreviated as FF. The Firefox project went through many versions before the version 1.0 was released on November 9, 2004.
In 2016, Mozilla announced a project known as Quantum, which sought to improve Firefox's Gecko engine and other components to improve Firefox's performance, modernize its architecture, and transition the browser to a multi-process model. These improvements came in the wake of decreasing market share to Google Chrome, as well as concerns that its performance was lapsing in comparison. Despite its improvements, these changes required existing add-ons for Firefox to be made incompatible with newer versions, in favor of a new extension system that is designed to be similar to Chrome and other recent browsers. Firefox 57, which was released in November 2017, was the first version to contain enhancements from Quantum, and has thus been named Firefox Quantum. A Mozilla executive stated that Quantum was the "biggest update" to the browser since version 1.0.