I'm using RHEL5 .While using firefox ,it automatically closes when any flash link or general link is clicked,not alwayas,but sometime.So I used flock ,the clone of firefox. Same thing happens here also.help me how to fix it ,what's the reason behind this ??

flash is the reason for all your problems, although it might differ from os to os. test this and if it works keep it: get the FlashBlock addon from firefox, then enter a site that usually crashes, if it works, it should work just fine from there on if you just click on the icon that shows where the flash app was supposed to be and it will run just fine.
Apparently (and this happened in my case, I may be the only person), firefox crashed when loading flash at the first load of a web page. If it was loaded afterward it worked just fine.
But then... there you have it, this is why we can't have nice things.

Fedora Development

Flash 9 for linux is buggy. Try Flash 7. Flash 10 beta is out haven't tried it.