By default, Firefox is configured to give only a 10 second delay for the execution of a script. Pass this delay and you will end up with a unresponsive script error message. It's quite annoying if you have a slow internet connection!
To increase the time allocated to script execution
In the address bar of Firefox, type :
Confirm the warning popup with the "I'll be careful I promise"
In the Filter field type: dom.max_script_run_time
Double click to modify the value (in seconds) for this entry