In the new refresh to the Fire TV UI, the primary navigation for things like Home, Your Videos, Movies, TV Shows, Apps, etc. has been moved from the left-hand side to the very top. Below that is a large area to showcase highlighted Amazon Original content, apps, movies, and more. However, rather than just featuring a still image of the content here, it's reported that this area of the UI will actually be able to play trailers for the content its advertising so users can immediately see if it's something that they'd be interested in. Below this section of the interface, both your recently viewed content and a customizable app tray will be present.
Additionally, the "Your Videos" section of the interface will supposedly showcase all of the streaming content that you have access to. However, Amazon isn't just including Prime Instant Video content and shows/movies you've purchased through them. If you subscribe to services like Netflix, Hulu, etc., those titles will be displayed their as well. It sounds like a great way to look at all of the video content you already own or subscribe to, and addresses one of the primary issues that Fire TV users have had with the current UI.
The new update to the Fire TV UI should be available to users at some point before the end of the year, and owners of the Fire TV Stick with Alexa Voice Remote and the newest generation of the Fire TV will have access to it first. However, Amazon will make the update available to older models of the Fire TV and TV Stick at some point later on down the road.