Webkit browsers, for the first time, have a greater market share than Firefox

W3Schools are based only on their own site, so a very particular market (i.e. web-developers I'd guess) while Statcunter brings in stats from their embedded counter on millions of sites so might present a better overall view (not that any sampling will ever be perfect for this!)

Wikipedia actually has quite a nice overview with stats from various sources: http://en.wikipedia.org/wiki/Usage_share_of_web_browsers . It does look like it is a general trend - this is the transition period for Webkit replacing Gecko as the number 2 rendering engine on the web.