hi, i had this problem of response delay time for alt-tab and ctrl-alt-del function. i tested it with ff4 for a few days and then downgrade to ff3.6, and to my amaze it is ff4 that is causing this.

when i started using ff4 for a long period of hours, and when i'd need to close a certain process in the task manager, after pressing ctrl-alt-del to get there, ill get a blank screen for 4secs before the task manager is out, its the same for alt-tab between other programs, i'm sure the culprit is ff4 as ff3.6 isn't giving me any similar problem like ff4.