The add-on cannot control the menu in any meaningful way. If you are willing to mess with userChrome.css, the following addition should do the trick - hiding the default option and moving this extension to the top:

/* Hides Open Image In New Tab */
#context-viewimage { display: none; }

/* Hides Open View In New Tab */
#context-viewvideo { display: none; }

/* Moves View Image to the very top */
menuitem[label="View Image"] { -moz-box-ordinal-group: 0 !important; }

/* Moves View Video to the very top */
menuitem[label="View Video"] { -moz-box-ordinal-group: 0 !important; }