This is basically how Mozilla began, as Netscape died, right?
Firefox was originally competing against the pile of steaming garbage that was IE6.
Now they are competing against Chrome which is actually a good browser, and Chrome also has the advantage of having google behind it which can leverage their search/ad monopoly to push Chrome.
And which they have shamelessly done.
The way I’ve heard the story is that by the time of firefox, IE6 was still a really good browser, it had just stayed stagnant for a little too long, and bundled got with Microsoft’s monopolistic behavior.
I think there are more parallels between late IE6 and present day Chrome then you give credit for.
To do this today, with a much more complex product would be no mean feat, back then a browser was a much simpler piece of software than it is today.
Netscape was not “still hugely popular” when Firefox was created. IE market share was upwards of 90%.