"why my mozilla firefox closes itself while working"
 

i am using ubuntu on my hp pavilion dv6000 notebook. since i have installed linux my firefox closes itself in the middle of some work. also my computer hangs a lot.

Well, since you don't post any useful information (like an error message, what web site you're going to, etc.), there's not much anyone can tell you.

When you are doing "some work", what sites are you going to? How did you install Firefox? What are you doing when it "hangs a lot"?? What version of Ubuntu?

I wouldn't ask for the exact site someone visits, let's be descrete at that point. Maybe a hint at what features are used (images, flash...) will do the job.
Rather than the version of Ubuntu, I'd ask for the version of Firefox. The problem looks like a bug in Firefox, so updates should be tried.

Specifically, this information could be useful:

• Did you try to update your Firefox? ("sudo apt-get update; sudo apt-get install firefox" in a console/terminal/shell)
• What version number ("firefox --version" in a console/terminal/shell before updating) were you using?
• Do you have a link where crashes happen in Firefox (the site shouldn't be offensive or something)?
• if not... What kind of features did the sites have (like, flash, media...)?

usually i visit sites like gmail,wikipedia n stuff but i think its the no of pages that concerns. when i open more then 5 pages or do some download work it just shuts itself.
my notebook also hangs usually after an hour or so if i am doing multitasking enen if my internet is disconnected. it does not show ne error it just stop responding. and the capslock light start blinking.

Well, there's no common thread between the sites (like everything using Flash 9, or having Java-heavy apps on them), so that's probably not the issue, unless you can think of something in common between what you're working on. As Titan suggested, have you updated your Firefox? I'm on 3.0.10 on OpenSuSE, and can have 5 or so sites up at once with no problems.

But the flashing capslock light...that's a bit telling. If you're off the net, and it doesn't respond at all, that removes Firefox from the equation, and points to something else. Does your system have a cooling fan on it, and is it running? The only times I've ever seen flashing lights like that, it's indicated a hardware problem of some sort, like overheating. How long have you had Ubuntu on that system? Sometimes ACPI won't play nicely, and things like the fans, etc., won't work correctly. The time also is a bit suspicious, since its always after an hour or so, which leads me to think it may be an overheating issue.

BTW we don't know if he is using Ubuntu...

In his first post he says:

SORRY I only read "I installed Linux" and didn't read his first sentence.