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?
There’s an article linked, perhaps it might give some insight.
So this build change actually originated in the upcoming Android 15, but since that codename had already been chosen they didn’t rename it to A.