Getting data to javascript and server script

I have a control called RollPanel that provides panel like functionality with the option to roll up the nested content and server controls.

The roll state of the panel is tracked across post back events.

Now here is the thing. Originally I used hidden fields created by Page.RegisterHiddenField to pass the data back and forth from the server side to the client javascript, this really screws up in FireFox so I had to scrap it.

I switched over to cookies. This works in FireFox, IE, and most likely any cookie enabled Css 1.0 ready browser.

Is it bad to use cookies? I never use cookies for anything I never have. I would rather use the hidden fields but Firefox has issue with it.... according to JavaScript FireFox changes the hidden field values but once a PostBack occurs they persist as the original values...

http://netnsite.com/zeke/rollpanel.aspx <~~~ see the control in action