in fact, ive got no idea why this may happen, except firefox being damaged in certain way (probably by using it too frequently, it simply wants to retire in honour), but obviously there are no system- or hardware-problems on your CPU (why should IE run that quickly if you had some...) and as it seems to be a firefox-problem i would recommend to deinstall and reinstall, maybe even an older version of firefox.
(Cacher) Si vous ne consultez que quelques uns des forums de discussions sur une base régulière, vous pouvez les ajouter à la liste de vos forums favoris en allant sur la page du Forum et en cliquant sur "Ajouter à la liste des forums favoris". (pauloaguia) (Montrer toutes les astuces)