I've got some good news for you. I've found a way how to fix it on the net. Read the explanation below. I've already done the settings as described and there are no such issues with my Firefox and Seamonkey browsers any more. Here how you should do:
To fix it, you’ll need to access the hidden configuration page in Firefox. Just type about:config in the address bar and you’ll get a page full of hidden configurations which you can tweak till your heart’s delight.
In the ‘Filter’ box, type dom.max_script_run_time. This will narrow the options till only the dom.max_script_run_time option remains. Right-click it and choose Modify. A box pops up. Change the number to something bigger like 20. This is the maximum time a script can run before Firefox considers it ‘unresponsive’.
If you can’t find the string in the about:config page, create it by right-clicking anywhere and then choose New—> Integer and enter dom.max_script_run_time. When prompted for the value, use 20.
Source: http://itchyhands.com/2006/01/07/fix-firefox-unresponsive-script-warnings/
for one troubling bug of Mozilla Browsers 
