For those with vision impairments the options you need to set to true in about:config are:
widget.gtk.global-menu.enabled
widget.gtk.global-menu.wayland.enabled
Presumably you would only need the second option if you are using Wayland. I tried it (am using Plasma on Fedora 42) and it worked but I'm not interested in it so I disabled it after I made sure all the menus gave a drop down. YMMV.
I got warned for "report abuse" after reporting a bunch of misogynistic comments on a sports subreddit.
Also, fuck spez.