1, the upper right corner of the menu - "Custom -" bottom left corner "title bar" to cancel the tick
2, if the above can not be solved, the environment variable is inserted before a start firefox, specific changes /usr/share/applications/firefox-zh.desktopfile, add the intermediate Exec middle row env MOZ_GTK_TITLEBAR_DECORATION=clientbelow
Exec=env MOZ_GTK_TITLEBAR_DECORATION=client /usr/bin/firefox-zh %U
Different versions of firefox firefox-zh at a position different from the above, only this time from the change start icon and launcher systems, plus additional commands needed to start the environment variables.
3, if it is not resolved to consider the relevant plug with it.