I reported this issue several times, email, github even twitter but apparently nobody from Docker Inc was able to address it.
If you try to access pages like https://docs.docker.com/engine/reference/commandline/network_ls/ with Firefox when your screen layout is portrait, you end-up with an impossible to browse experience because sidebar suddenly expands to take your entire screen. This happens even on a 5K monitor if you resize page to take 1/2 of the screen.
This screenshot should explain it well:
You can even reproduce the problem yourself using Firefox by resizing the browser window to make the width smaller relative to the heigth.
When this happens is impossible to access documentation content, only the menu is visible.
Ironic, if you lower the height of the page to ~1/3 the sidemenu will repair itself. I really doubt this is a Firefox bug.
PS. The get support button is useless, nobody replies to reports made there.