When I start Firefox, I have no problems for a while, but after a couple of days, CPU spikes start to occur. During a spike, Firefox freezes and then stops. Spikes occur every seven to ten seconds, and each spike lasts for two to three seconds. If I am typing when a spike occurs, characters output only after the spike. I initially thought this problem was because of Flash, so I disabled it, but the problem still occurs.
Also, Firefox's memory usage increases to over 600 MB after several days.
The list of Firefox plugins and extensions I use is available here.