Opera and Amazon site problem solved
Are you using Opera, the best browser on Earth? If yes, and if you experienced problems on Amazon, then this will help you!
The new version of Opera (12 at the time of writing) works with Amazon ONLY if you accept all cookies. I had the site preferences set to allow only cookies from the domain, which killed all search results and login features.
There is no nee to spoof the user agent. Identifying as Opera works just fine, but remember to allow all cookies!
Hope this helps,