Hello, On random websites and moments, I notice Firefox using 25%CPU. I have 4 cores. I don't know what's causing it, and it is pretty annoying. It just hangs and becomes unresponsive for about ~ 30-45 seconds. After that it happily continues without problems. It doesn't actually crash, it only hangs. I think it's something with an extension that's causing it. I have this as well on my laptop, that has Hyperthreading. (this PC doesn't) - On the laptop it uses 13% CPU when the same issue appears. I have Firefox 5 fully updated. Addons I use: Ghostery Adblock Plus HTTPS Everywhere WOT (Web of Trust) I use on both computers Windows 7 Professional. One of them is English, the other Dutch. Both legal and with all updates. I also have the Flash and Silverlight plugin, up-to-date. If there's any other information you need please let me know. Would like to have the issue resolved :) Thanks, Niels