[Unity 5.6] Window -> Lighting -> Scene doesn't exist for me

I am trying to turn off the horizon. In questions like this: Unity 5 removing horizon in the background - Questions & Answers - Unity Discussions I am told that I need to go to Window → Lighting → Scene. However, this option does not exist on my system! Here is what the Window → Lighting menu looks like for me:

I’m running Xubuntu 16.04 LTS 64-bit with Unity 5.6.0xf3Linux Personal 64-bit (as shown in the screenshot). I really have no idea what to do.

Unity Editor for Linux is only experimental, and not fully supported like Win/Mac yet. I’d recommend posting questions about experimental features like the Linux editor in their specific forums, rather than in the general Answers area where people will expect you’re using a supported Editor build.

Here’s the forum for the experimental Linux editor:
https://forum.unity3d.com/forums/linux-editor.93/

I have no problems getting to this setting on 5.6.0f3 for Windows by the way.