No scrolling possible in API browser until window is resized

[Talkless]

Here's video on Firefox in Mobile (Ctrl + M) view mode (same in normal mode):

Kazam_screencast_00002-2.mp4

At first, content is longer than vertical space of browser window, but I cannot scroll it down in any way (down-selecting and mouse wheel has no effect).

Then, I resize window a bit, and after that scrollbar immediately appears and now content can be scrolled.

Same issue on Android Chrome.