How do I prevent XFCE freezes when running OpenGL?

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Whenever I run TF2 from steam, about every couple of minutes or so it freezes, and then in about 15 seconds it unfreezes. The freezes are random. And, from my CPU usage monitor in my menubar, I can see that the CPU usage drops off rapidly at the points at which it freezes. My graphics card is a second generation intel family processor, and I have updated my drivers to the newest version.