Firefox is the spiritual successor of Netscape Navigator, as the Mozilla community was created by Netscape in 1998, before its acquisition by AOL. Firefox was created in 2002 under the codename "Phoenix" by members of the Mozilla community who desired a standalone browser rather than the Mozilla Application Suite bundle.

The Firefox project has undergone several name changes. The nascent browser was originally named Phoenix, after the mythical bird that rose triumphantly from the ashes of its dead predecessor (in this case, from the "ashes" of Netscape Navigator, after it was sidelined by Microsoft Internet Explorer in the "First Browser War").

https://en.wikipedia.org/wiki/Firefox

On January 23, 1998, Netscape announced that its Netscape Communicator browser software would be free, and that its source code would also be free. One day later, Jamie Zawinski of Netscape registered mozilla.org. The project took its name, "Mozilla", from the original code name of the Netscape Navigator browser—a portmanteau of "Mosaic and Godzilla", and used to coordinate the development of the Mozilla Application Suite, the free software version of Netscape's internet software, Netscape Communicator. Zawinski said he arrived at the name "Mozilla" at a Netscape staff meeting. A small group of Netscape employees were tasked with coordinating the new community.

https://en.wikipedia.org/wiki/Mozilla

Everything that was useful in Netscape became the basis for Firefox.

See also the documentary.