They could name it Firefox XP, I guess. All silliness aside, I see your point. But is the browser really still at a point where such earth-shifting changes are

They could name it Firefox XP, I guess. All silliness aside, I see your point. But is the browser really still at a point where such earth-shifting changes are likely to occur? The biggest single change of the last few years that I can think of is the addition of tabs to browers, and even that is a feature that's been around for 20 years in other programs. Any change that's much bigger than that almost warrants a whole new product, regardless of your numbering scheme.