Q:

The document.title is NOT Document 

ok, this is weird, and I like to have an idea if this is possible
e.g.
the page
<title>12345</title>
then if js is if(document.title=='12345')...
I guess this must be true, BUT my counter tells me otherwise, 10% is NOT (most in IE)
So I like to know, is there any browser plugin or other stuff does this and make document.title is NOT <title>

A:

Try logging what document.title is if it isn't '12345'. 
The most likely thing is if the file is being transferred with chunked encoding (a common feature in HTTP/1.1) then the <title> tag may be split in half and this would cause an incorrect title to show up. 
This can be fixed by adding:
window.onload = function() {document.title = document.getElementsByTagName('title')[0].firstChild.nodeValue;};

