By default, Firefox gives Javascript scripts 10 seconds to run. If the script takes longer than that to run, Firefox will assume the Javascript code is hung and it will give you an error message about the script being unresponsive. Some sites that are really Javascript heavy and that have large pages can legitimately take longer than 10 seconds to run, so this error message is really annoying since it keeps the page from loading correctly. If you want to increase the 10 second limit, you can.

In the address bar of the browser, type in about:config and get past the warning message (Firefox 3 users only). Once in the config editor, find the entry called dom.max_script_run_time and double click on it to edit the value to whatever you like.