I'm having an issue where I right click and as soon as I release the button, it selects the option where the mouse is like I left-clicked. Also, context menus are appearing in the middle of where my mouse is. Attached is an imaged that shows what I'm saying:
I don't know if this is an firefox bug or not but there are more topics about this
Also what version of firefox are you using? I have version 62.03 and got no problems with the mouse button/context menu for now.
Edit: got a litte fix go to -> about:config and change ui.context_menus.after_mouseup to true This fix the problem for now