MacBook 2Ghz: If it's charging, the fan is pretty much on most of the time, which makes sense since the battery gets quite hot during charging. If it's fully charged, not so much.
On battery power the fan rarely comes on, but there are a few things that can get it running. Video is one; online or offline.
FireFox has had some memory leak issues, but browsers in general have a lot of configuration options, and broadly speaking the defaults are all set to the most power-hungry, cache every-damn-thing settings, to make their browsers appear fast. All of which are eating up cycles and hard drive access, and all of which can easily load up any computer.
Like browsers, OS's and applications are all eager to do stuff in the background to make themselves look faster in the foreground. How many and what background apps do you have going? If you have fancy screen savers, your desktop is you kid's grad movie, and it's checking for mail every minute, you are going to generate heat.
If you want the fastest, coolest running computer, no eye candy, no fancy 3rd party "enhancements" and go through your preferences turning automatic-this and check-every-these-minutes-for-who-knows-what off.
The short answer to : "... is Firefox heating up my iBook?" is yes, of course it is; that's pretty much exactly what every application does. You only need to worry if it's heating it up too much.
Personally, I let the heat go where it may and as long as I hear a fan either all the time or occasionally, whatever is normal for that machine, I know it's working so that is fine with me. I've yet to own a Mac that I didn't work hard and didnt' get 6 years of daily use out of; the old version of Tech Tool Pro used to be able to report total hours of operation (saved in PRAM) and I was past 14,000 hours on my first PowerMac before it reset to zero with a PRAM battery replacement.
Since 1995 I've only just now bought my third new Mac, and it's a laptop; the second desktop is still in daily service. *
I've always ignored heat worries about regular, normally working computers (overclocking, insufficient clearance, dust or the cat blocking vents, fans screaming blue murder, etc is not normal and another matter altogether).
It probably has something to do with my experience with power amps that were too hot to touch, stuffed into closets in the farthest, darkest corner of bars in night clubs, and still worked for years despite the neglect. Of course they have to be built properly for that to work, no Phase Linear gear need apply, but it's hardly impossible or even unusual.
CPUs are made to take a lot of heat; they are amongst the hottest running devices ever designed by man. Too much is truly too much, but up to the design temperature they are fine, even if it does feel hot on your thighs.
Google's recent white paper on hard drive failures found absolutely no correlation between hard drive temperatures and the failure rate within the high range of normal (40~50 C) versus low range of normal (30~40 C), and they use off-the-shelf consumer grade drives from all makers. If the drive overall is running at 40C you can be sure some parts of that drive are running much higher than that.
* Actually I've had 5, but two were quickly replaced with better machines after owning them for less than a year.
Last edited by gordguide; Feb 28th, 2007 at 02:47 PM.