Stays for me, where are you trying to place it ?

Why not try changing the firefox layout, as you can see from my image (I have a minimalist layout to give more space), I don’t have the menu bar displayed - you can get it using the alt key if you need it. I don’t know if that may help or not or if you are already doing that.

I also use the Nuvola theme, which is a smaller compact theme.