When using an Ajax UpdatePanel, everything seemed to work fine on different flavors of IE, but when used on Firefox and I would hit the Refresh button, my postbacks seemed to stop working.  I checked into the javascript error that was coming up which said

"The state information is invalid for this page and might be corrupted"

After a bit of research, I found a post (do not recall where), that mentioned this is an issue with the way Firefox caches viewstate.  There was several suggestions ho to handle this, but most would be a security risk.

Finally, I spotted one that mentioned he added a:

Response.Cache.SetNoStrore()

on the the page load and it worked for him.  Another followup post said they included filtering out so that this is only set on Firefox:

if (Request.Browser.Browser == "Firefox") Response.Cache.SetNoStore();

For me, using Visual Studio 2008 Pro with IIS7, and IE7, this still did not work.

I found another post that mentioned using:

Response.AppendHeader("Cache-Control", "no-cache; private; no-store; must-revalidate; max-stale=0; post-check=0; pre-check=0; max-age=0");

I put that into my "Page_Load" with a check for Firefox (like above) and presto, the error vanished!

So, if one method does not work for you, give the other a try.