I was a contributor to a little pair of libraries called KHTML and KJS, a HTML renderer and JavaScript interpreter. Joined about a year into the project and while I didn't lay the foundations I helped improve the DOM and JS support a fair bit.

People I respected told me I was wasting my time because Internet Explorer was the de-facto standard and the idea of a new browser engine becoming prominent was fantasy.

Then Apple decided they wanted do a browser and looked around at what open source engines were available they could use as a starting point. Thus was born WebKit [1].

I consistently ignore anyone who tells me I shouldn't try something because it's "too hard" or "nobody will use it". Most of the time they turn out to be right. But not always.

[1] https://marc.info/?l=kfm-devel&m=104197104218786&w=2

Edit: Here's an interesting presentation by Lars Knoll and George Staikos on the history of the project: https://www.youtube.com/watch?v=Tldf1rT0Rn0