After updating to jQuery to version 1.3 my old script start killing Firefox and cause IE error.

Try to run this code with jQuery 1.3:

$(function(){
    $("#main LI:not(.current) A").css("background-color","gray");
  });

With HTML:

<div id="main">

<ul>

<li class="current"><a href="#">Current</a></li>

<li class="item"><a href="#">Item</a></li>

<li class="item"><a href="#">Item</a></li>

</ul>

</div>

And you get Firefox fail. IE with text:

"Stop running this script?

A script on this page is causing Internet Explorer to run slowly. If it continues to run, your computer may bacome unresponsive"

Chrome works fine.