Opera pages not liking Opera?

[Anonymosity]

Why do some pages for extensions for the Opera browser not load with Opera, unless I mask it as Firefox? With Firefox, there is no problem. With Opera sending a user-agent as itself, I get a 404 error.

These are 2 pages where that happened:
https://addons.opera.com/en/addons/exte ... oredirect/
https://addons.opera.com/en/addons/exte ... director5/

UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:10.0.2) Gecko/20100101 Firefox/10.0.2

[Antony]

server misconfiguration?

UserAgent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.7; en-US; rv:1.9.2.27) Gecko/20120216 AlexaToolbar/alxf-2.14 Firefox/3.6.27