Mozilla tossed the Netscape 4.x codeb ase and started nearly fresh with Gecko and then re-wrote components one at a time around that new foundation. It took a f

Mozilla tossed the Netscape 4.x codeb ase and started nearly fresh with Gecko and then re-wrote components one at a time around that new foundation. It took a few years, but the results were Mozilla 1.0 and Firefox 1.0. 10 years later Mozilla re-wrote much of Gecko and Firefox around a new multi-process architecture and new rendering and style pipelines for Quantum. Gecko is now about 25 years old and still used by hundreds of millions of people and is one of only three web engines today capable of rendering enough of the web well enough to be viable. We have Blink, Gecko, and Webkit and that's it. Blink and Webkit share a very large amount of legacy code, so Gecko is really the only decent alternative, at least from a more academic standpoint. (Want to study two independent implementations of the web platform, blink and webkit isn't really ideal, but either of those and Gecko would be.)