Rules block Amazon.co.uk and Amazon.de from playing MP3 previews
When you visit the MP3 Music store on Amazon.co.uk or Amazon.de, pressing any of the play buttons on music previews doesn't play sound. Disabling the HTTPS Everywhere add-on resolves the issue. Amazon.com works fine, so I think this is a fault in the rules for the non-US Amazon websites.
I'm on Firefox 17.0.1 on Linux. HTTPS Everywhere add-on version 3.0.4. I've had this issue for over a month, and finally confirmed it today by disabling all my add-ons except HTTPS Everywhere (no sound played for non-US Amazon websites) and then also disabling HTTPS Everywhere (now all Amazon websites play sound).
As an example to help reproduce, here are links to same album on Amazon.co.uk, Amazon.de and Amazon.com. Only the last one will play sound when a play button is pressed with HTTPS Everywhere enabled. http://www.amazon.co.uk/The-House/dp/B003LWGU7G http://www.amazon.de/The-House/dp/B003L15KE6 http://www.amazon.com/The-House/dp/B003WUG1JY