After spending the better part of a year working with web design, I can only pray that this trend continue.
Although impressive, it still has a long way to go before being considered dominant.
A good question might be: why hasn't it gained more popularity over the last 5 years?
Simple answer: big companies haven't switched to FF. If they started switching, their employees would go home and switch too. Until then, it will be hard to become a majority.
Simple answer 2: many people don't know or care what's a browser. For them using the internet is clicking the blue e icon that is there by default.