I looked on the download.mozdev.org and I no hotmail-1-4-1.xpi. Your probably mean webmail-1-4-1.xpi. I looked inside the hotmail-1-3-3.xpi and it updated to TB5 installable.
Here are the links to the web-mail author Google Docs pages: Webmail 1.4.1 https://docs.google.com/leaf?id=0B12SpPN0s2lAYmQwNWMyMWMtZGEyMS00M2ViLWJiZTktNmMzNGI5MTE2YWY5&sort=name&layout=list&num=50 Hotmail 1.3.3 https://docs.google.com/leaf?id=0B12SpPN0s2lAZTg4ZmJlNTYtMDMzYS00ZTdmLWI0ODEtZWUzYzM3ODBiOGIx&sort=name&layout=list&num=50 Eugene
