unfortunately, this is not how it works. When I log on to the US web store with a German user ID, I only get a message like "your account has a non-US billing address. Sorry, we can not sell anything to you"
Also, the German appstore is a bit different to the US one - it can only be accessed from the android device itself via the shop application, not online. And the support people at amazon.de said that the 1st generation Kindle Fire is "one of very few" android devices that are.not.compatible with the amazon.de webshop.
Sigh. I had hoped to finally be able to avoid the extra charges for the virtual www.usunlocked.com
credit card that I need for app purchases (and always changing between the two addresses that have that credit card and my "real" German credit card that I use for buying books).
PS: I had already planned to put my old Kindle Fire on eBay. But upon testing my long-awaited Kindle Paperwhite, I now know how good the Fire (even the old non-HD one) really is for nighttime reading, so there is no way I will get rid of that now.