Former programmer, Jamie Zawinski, also a founder of Netscape and Mozilla, has observed that Netscape Navigator 2.0 was released 30 years ago [jwz.org]. Netscape's full feature set existed identically on Macintosh, Windows, and nine flavors of Unix, something which was basically unheard of at the time.
Netscape was finished off by a double hit. First, Microsoft illegally abused its desktop monopoly to enter and crush the browser market [justice.gov]. Second, and probably even more detrimental, they got taken over from the inside through what should have been an acquisition of another, smaller company [cnet.com].
The remnants are known as Mozilla. That is a separate story.