There is a great challenge between Google and Mozilla to update their browsers deeply!
When you trace updates of chrome, you realize that it jump from 1 to 2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,... very very quickly!!!
The Mozilla Firefox was intellectual b4, but nowadays it feels under pioneer, so Mozilla go faster to update their browser Firefox one by one! (3,3.0.1,...,3.6,4,5,6,7,8,9,10,...). BUT the difference between versions of Firefox or Chrome are very negligible!
When a new user of Internet wants to use a great browser, he/she prefer to browse with the higher versioned browser probably!!!