I used to have this problem some while ago and got rid of it by editing the userChrome.css and adding this bit of code: #PlacesToolbarItems .openintabs-menuitem, #placesContext>menuitem[id="placesContext_openContainer:tabs"], #placesContext>menuitem[id="placesContext_openContainer:tabs"]:not([hidden])+menuitem+#placesContext_openSeparator {visibility:collapse!important} Sadly though, this doesn't seem to work anymore as this bothersome menu item has recently returned, just waiting for me to accidentally click on it again. So yeah, is there any way to get rid of it once more, hopefully for good this time?