I had precisely this problem. I can confirm that the problem is solved bvy leaving DeepGuard enabled and only disabling the suboption "use advanced process monitoring. Firefox 14.0.1 F-Secure Internet Security for Windows 9.16 build 131 Windows 7 Enterprise SP1 x64 The process that starts maxing out on cpu is plugin-container.exe. Should be easy enough problem to recreate, and a bit of Googling turns up plenty of other people having the same problem.
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