Firefox has a CPU usage issue and, consequently, can cause overheating problems in some laptops, particularly ultraportables.

The Mozilla support page goes on to say that "you can review and monitor CPU usage through specific tools" and describes ways to limit CPU usage, such as: "A Firefox add-on, called Flashblock, allows you to selectively enable and disable Flash content on Web sites."

Let me describe my experience. I find that tab for tab, Firefox uses decidedly more resources than other browsers--Safari, for example. And in the past (when I was actively using a Windows Vista-based machine) Firefox also compared unfavorably with Microsoft's Internet Explorer for CPU usage.

More specifically, here's the behavior as I see it. When I'm accessing sites with multimedia content such as the CNET front door, Firefox CPU usage will bounce around between 30 and 60 percent, and sometimes spike higher (80 percent and above), as indicated by the Mac OS 10.6.2 Activity Monitor.