I have seen this thread in two forms: firefox using too much CPU and Firefox using too much memory. I have tried all the suggestions listed in what threads I can find, including running in safe mode. Basically, I run FF version 3 or 4 and it runs fine. I upgrade to Version 6 or 7 and immediately upon start up, Fire fox consumes 45% of my CPU cycles, 200,000k + of my memory, and 100+ handles. Open up 2 tabs and it rockets to 60% CPU, 300-400,000k memory, and 2-300 handles. Each site takes between 30-70 seconds to load, even local ones. It continues to grow the resources slowing the browser down even further as it is used. I downgrade to version 3 or 4 or 5 and it's back to normal.