Mozilla (Javascript) eats my CPU and memory

Every once in a while Mozilla (Netscape), typically via Javascript, just eats up my CPU and/or memory, rendering my box just unusable. (In particular, Netscape says that a web page is slowing down Netscape. Or it starts to say that. And then it give me options that, because the system is so slow can't be selected.)
Can I set anything in about:config to get around this? Is there anything more general that I could do in the OS configuration?
Thanks.