To reproduce:
1. Open any project
2. Open build settings
3. Click "Tizen", "PS Vita" or "PS4"
4. Click "Open download page"
Notice that it directs the user to a non-existent page.

Reproduced on:
5.6.0b3 with Tizen, PS Vita and PS4, not reproduced with Facebook Games and Samsung TV
5.5.0f3 with PS Vita, PS4, not reproduced with Tizen, Samsung TV
5.4.2f2 with Windows Store, PS4, PSP2, PS3, XBox360, not reproduced with Samsung TV

On windows, these links open as expected.

Not tested on 5.3 or earlier because a button like that doesn't exist in those versions (instead it's a button that opens the Module Manager).
Note: on each of these versions, the "Go to download page" button for xbox one just links to a blogpost from 2014 ( https://blogs.unity3d.com/2014/08/11/unity-for-xbox-one-is-here/ ), I am not sure if this is intended or not.