Mozilla, the free software community founded by Netscape, is a portmanteau of the words mosaic and killer.
Jamie Zawinski, an employee at Netscape, came up with the name, apparently a shortened form of "Mosaic killer," and the name became the internal name for the Netscape browser. The name represented the company's goal to displace NCSA Mosaic as the world's number one web browser.
The company adopted a Godzilla-like lizard as mascot which evoked the sense of their goal to crush the competition, as well as sharing a similarity with the name.
Sources: Netscape announces Mozilla.org | Wikipedia