According to Statcounter.com's current numbers, Chrome is 36.9%, Safari is 8.57%, and Opera is 1.2% = 46.67%, leaving 53.3% for everything else. That's not "roughly two thirds".
Also, Safari and Chrome are both trending upwards, everything else is trending downwards.
http://gs.statcounter.com/#browser-ww-monthly-200807-201302