Amazon's newest Fire TV Sticks are dropping support for normal sideloading, blocking apps from outside the Amazon Appstore unless the device is registered with developers. Cord Cutters News reports: This week, Amazon announced the upcoming launch of a new Fire TV Stick HD. The new model will run on Amazon's Vega OS, rather than Android, so most streaming apps will be supported, but users won't be add third party apps. Now, on the product page to preorder the new Fire Stick, some Amazon customers are getting a message warning them that the new model won't allow sideloading. Interestingly, not all customers are getting the message, whether signed in to an Amazon account or not. The message, shown in a screenshot below, says: "For enhanced security, this device prevents sideloading or installing apps from unknown sources.…