This is a well known problem with the latest re-incarnation of Hotmail, following it's change from MSN Hotmail to Windows Live Hotmail and is caused by Microsoft having employed browser sniffing technology to ensure that Hotmail can only be accessed by Internet Explorer, Firefox or Safari.
There is a long discussion about this on the Opera help forum which contains various suggested "work arounds", none of which really work.
Read at
http://my.opera.com/community/forums....dml?id=255068