I have recently been debugging a few websites that have javascript functions that run on every page load (including ajax postbacks).
Traditionally, you would use sys.application.add_load to achieve this. However, Firefox 3 appears to only run functions assigned to this after postbacks and not on the additional load.
Now it would be easy to use jQuery's document.ready to run the function on the first load in addition to the sys.application.add_load call, however, this seems to me to be a little 'hacky' and would mean that your function runs twice on the first page load!
Luckily, Microsoft already have a solution to this in thier .net javascript code. All you need to do is rename the function that you need to run on pageload/postback to pageLoad and it automagically works in all browsers! Great huh!