And ultimately a huge waste of time. It set back Netscape and Firefox development for several years. Meanwhile IE6 took over, leading to the web dark ages while Mozilla reinvented the world.
For more details there is the famous Spolsky post about things you should never do—rewrite a product from scratch. Mozilla went one further and tried to reinvent GUI programming as well as building a new product.
It's famous that Mozilla and Firefox went through many rewrites and stalled progress. But I don't think you can blame that for IE6. Some amount of that is due to the Windows monopoly and that it was preinstalled.
Right, so, in that period, IE stagnated, and so did Mozilla. But IE was the dominant stagnant browser and not Mozilla or Firefox. That's somewhat on the monopoly.
In much of those days I used Netscape 4.x and it really wasn't much worse than IE. Then I used pre-1.0 Mozilla and various forks, and early firefox, they were all pretty acceptable for the time. The big issue was that all the content was authored for IE and not tested anywhere else. Monopoly.
Yep, I used Communicator for many years. But it always drove me nuts that it couldn’t resize the window without redoing the whole page from scratch. The new Mozilla browser took years to stabilize. It was frustrating chapter for the web... the bad old days.
For more details there is the famous Spolsky post about things you should never do—rewrite a product from scratch. Mozilla went one further and tried to reinvent GUI programming as well as building a new product.