I am not quite sure whether this thread belongs to this section of the forum, so please relocate it if necessary.

Being in the habit of viewing source from web pages I come across every day, I could not but notice a rather too ubiquitous script reference that seems to plague the otherwise correct code as reported by the Firefox HTML Validator extension. It runs thus:
<script language='javascript' src=''></script>
I am quite sure that it is somehow generated on the spot and not a part of the original code. The numeric part of the URL I recognize to be equivalent to localhost, but I do not know what to make of the js.cgi? and the variable part that follows.

Is it server- or browser-generated, and does firewall software have anything to do with it? I am at a complete loss to understand it.