Google has begun serving a different YouTube interface when the video-sharing website is loaded by Firefox on an Amazon Fire TV device. The different interface, spotted by the awesomely named Reddit user Swole_Chicken, is functionally identical to the interface YouTube usually serves, but consists of a slightly different navigation layout.
To view the different layout, you must load youtube.com/tv in Firefox with its new Turbo Mode enabled. Loading YouTube in Firefox with Turbo Mode disabled, in the Silk Browser, or through the still functional old Fire TV YouTube app will result in the older YouTube interface. If you have Turbo Mode enabled and are not seeing the different YouTube interface, you’ll need to clear Firefox’s app data in the Fire TV’s settings section.
I don’t know if the different YouTube interface is a newer interface that will eventually replace the previous interface for all television browsers or if the different interface is an unintended artifact of Firefox’s Turbo Mode blocking certain scripts required to render the usual YouTube interface. Either way, the two interfaces don’t differ too much, so I expect some will prefer the usual interface while others prefer this different interface.
The main difference between the two YouTube interfaces is that this different one tends to use a vertical sub-menu where the usual interface uses horizontal menus. Most differences are found while browsing for videos since the player interface is the same in both cases.
As previously mentioned, the two interfaces are functionally the same and don’t affect how YouTube videos are played. The exact same settings are available with both the different and usual interface. Both interfaces still do not play video in 4K on capable displays.
For better or worse, Google controls the interface served for YouTube since all implementations of YouTube on television hardware, even non-Fire TV devices, has switched to using a web view instead of a native app. For the time being, you have a choice between two interfaces, which is a rarity, but don’t be surprised if one of them eventually changes to match the other.