Firefox hangs with Error: Unresponsive script "ScriptResource.axd"

Hi,

all of a sudden (I think after installing latest Windows Patches on the Server) a form opened in Firefox brings a warning of an unresponsive script like:

Skript: http://www.barni-post.ch/ScriptResource.axd?d=kTetbmQtysF6lXGYQN1TFLUYgcuwUCKTSuv7QIfEASQd9l7Hpp-eI6qUZC0uFbOVS-MBWUBVez2GbIskUOTiTgf9jSFz84UtTP21LNOOX0iOvG2Wza19w72VChT5GdE6X5FV08p4Yl12Z0FPPUuqKg2&t=252a36c5:1

the form (http://www.barni-post.ch/service/inserat-online-aufgeben.aspx) works just fine in in IE and Chrome.

I found some similar posts, pointing to the direction of turning off compression, but could not get this working.

What can I do to get this fixed.

Thanks

Christian