A classic Joel Spolsky post that completely failed to take into account the fact that Netscape rewrote itself into Mozilla, which then went on to eat IE5's lunch.
I'm a big fan (and user) of Mozilla but this take seems wrong to my memory.
Checking Wikipedia, the IE5 timeframe was them reaching their peak before stalling on the infamous IE6, and Firefox (sort of a rewrite of the rewrite) starting to make some small headway as they let IE stagnate.
Usually you cannot count on competitors to stop all developmet for half a decade while you rewrite.