Firefox: disable “send link/tab to device”

So you'd have to type this on userChrome.css The first class removes the actual command, and the second of each line remove the separator so that it doesn't look like there is something missing on the context menu.

#context_sendTabToDevice, #context_sendTabToDevice_separator  {display: none !important;}

#context-sendpagetodevice, #context-sep-sendpagetodevice  {display: none !important;}

#contentAreaContextMenu #context-sendlinktodevice,
#contentAreaContextMenu #context-sep-sendlinktodevice {display: none !important;}