For YouTube it displays the YouTube menu on first right-click, then the Firefox context menu on second right-click for me. On Windows.
If that is not the case for you, something may be broken. Have you tried running Firefox without any add-ins already?
I made a small handle on the edge of my screen to toggle auto-rotate with One Handed Operation+
I’m not sure how well it works on non-Samsung phones, but I wouldn’t want to use my phone without it.