When I open the Updater I do not see the dialog that is described in https://imagej.net/Updater. Instead I get the following dialog without a list of files and buttons to choose the Updater mode. Because of the lack of buttons/lists there is no way to add update sites (which is what I need to do).
Latest ImageJ available as of 8/29/17 (Fiji distribution)
high resolution monitor (3800 x2160… also tried lower-res settings)