Investigation revealed that things were as described by the customer. When in Facebook, the computer was slow and unresponsive, as well as noisy. Switching to another website immediately caused it to become more responsive and quieter. Generally speaking, most of the noise on a laptop comes from the fan, and if the fan is on constantly then it is to prevent over-heating. This indicates that the processor is working hard, which causes it to generate a lot of heat.
Further investigation revealed that the problem wasn't Facebook per se, but rather was being caused by Adobe's Flash player. Most computers have Flash installed; it is used extensively by many websites and is responsible for handling animations and video (including many of those annoying adverts). It is also used for developing games, and it turns out that the user had a Flash-based game within Facebook. It was causing the processor to run constantly at 100% utilisation, making it overheat. Fortunately there was an easy fix in this case - updating Flash caused it to behave a lot better, making it run with far less CPU utilisation.
Although Flash is widely used, it is not without its critics. An important one was the late Steve Jobs, chairman of Apple. He disliked it so much that it is banned from the iPad altogether. There are three main reasons for people being opposed to Flash. Firstly, the example quoted above is not an isolated incident; Flash can be a CPU-hog. Not only does this slow a computer down, it also drains the battery more quickly on a laptop, tablet or Smartphone. Secondly, there have been many security vulnerabilities with Flash. To their credit, Adobe quickly identify them and update Flash on an aggressive basis, but it is perceived as a security risk. Finally, it is in real danger of becoming obsolete.
To understand the last comment, a little history lesson is needed. When the World Wide Web was new, web pages were text only. A few years after that, internet browsers gained the ability to display pictures as well when NCSA Mosaic (the grand-daddy of all browsers) was developed. Some years later, software developers began to produce "add-ins" - small, additional programs that gave browsers the capability to play sound, music, animations and video. It is important to remember that early browsers were incapable of doing such things on their own, and without the likes of Flash and Shockwave (another, related program from Adobe) then web pages would be rather dull indeed.
Fast forward to the present and the idea that a browser needed a separate program just to, say, play a video seems rather quaint. Web pages are written in a language called HTML and the current version - HTML 5 - includes a video specification. Browsers that are HTML 5 based can play videos natively and efficiently, without the help of assistants such as Flash. Most modern browsers understand HTML 5; to see if yours does go to Google and start typing in "Do a barrel roll". Pretty cool, eh? (if you are running Internet Explorer 8 you'll have no idea what I'm on about!).
What this means is that the future for Flash looks bleak. Adobe have now bowed to the inevitable and have announced that there will be no future development for Flash on portable devices such as tablets and Smartphones (remember, Flash can be a battery killer). Although it is business as usual for now with the regular PC version of Flash, don't be surprised if it too dies the death. Another casualty is Microsoft's competitor to Flash - Silverlight. Silverlight is in many ways a superior alternative to Flash and Microsoft have expended a lot of effort on it. However, they too have sounded it's death knells.
Steve Jobs would love it...