My browsers keep collapsing!

I have a MacBook and am running Tiger Mac OS X 10.4.6 and no matter what browser I use, my browsers keep closing occasionally when I click on a link to enter a website. The page will be loading and suddenly, in the blink of an eye, the browser will have quit and I'll get a prompt to retry. When I retry, I have to be sure and x out of the troublesome link or it will do it again indefinitely. This started out being very rare and has become very often lately.

What is the cause of this problem and what can I do about it?

 

I am using Opera, Safari, and Firefox. But the guy at the Mac TLC store said this sounds like a problem with the computer itself, not with the browsers since it does it with all of them.

And how do I update to 10.4.11? Can you provide a link?