I had a problem with Firefox and traced it to the Java Applet Plugin which was periodically hogging 99% of the CPU cycles. It was also causing things I typed to be jumbled. Exiting Firefox and restarting often took care of the jumbling but almost always the plugin started hogging recourses. For some things I needed the Java Applet Plugin so I tried “nicing” it from Windows Task Manager but as I suspected that feature of Windows sucked. So that and some of the security issues I found caused me to switch back to IE.
I found this link a little helpful when trying to figure this out. http://support.mozilla.com/en-US/kb/Java...g_in_text_boxes