Those buttons are not displayed, ever. Even if I enlarge a picture on a Google image search, the buttons are not displayed.
If I approximate where the buttons are, and click, the function works, the buttons are just not visible. There is a solid black rectangle there.

Annoying.
Note: I recently had a Trojan virus that installed ‘Binki’ and “Intel-something” which I have removed using Malwarebytes.
Prior to that, I had returned Firefox to the original installation.