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.
(nascondi) Puoi inviare un messaggio ai tuoi amici con un solo click aggiungendoli alla tua lista degli utenti amici e poi cliccando sulla piccola busta accanto al loro nome. (pauloaguia) (mostra tutti i suggerimenti)