#Firefox tip: if you open the context menu with a right click and then another click to activate the menu item, you may find that Firefox will activate whichever menu item your cursor happens to be over when the menu opens. This is really annoying for me. I've worked around that previously with a userChrome.css modification to offset the location the menu opens in, but it stopped working. I've found that setting ui.context_menus.after_mouseup to "true"
also works OK for this problem: it opens the menu *after* you release the right click, so there's no unintended activation.