Does the Mozilla Crash Reporter pop up? If so, go to the address about:crashes and tell us your latest crash IDs. We can then look at the data specific to your crash and have a better idea of what is causing the problem.

Well... I didn't report the crash and closed the window. So it will take another 8 hours of downloading to the next one. I'll try...

I installed an apache webserver for faster local downloading and put a 4GB DVD up.

First try on Windows7: After 500MB of downloading it stops with a memory load of 1.6GB then it suddenly tells me the download is finished - at 500MB of 4GB. No crash this time but still not the desired result.

Try on Windows Vista: After 1.5GB of downloading and 1.7GB of memory usage and then the CPU activity jumped to 100% on the core where Firefox executes. Took around 5min then CPU goes down to 2% and it tells me the download finished and starts a virus scan. No crash either. Downloaded only 1.6GB of 4GB

Maybe it didn't crash this time because the download is too fast. Earlier while downloading from internet it always crashed while downloading debian DVD image. Later I used Internet Explorer to complete the download. I'll install a bandwidth control in my apache and try again over a longer period of time.

I found the culprit. The only addon installed: Firebug!!!

This looks to be a bug that was introduced in some later version. I use this addon for about 2 years now and never had such problems. I'll contact the author of this addon.