The XNAT web application requires applets for a few of it’s features, particularly the image upload, image download and session timeout indicator features. However, support for java applets from the major browsers is being withdrawn. They are no long supported by Chrome or IE. The only hold-outs, at least for now are Firefox and Safari (with some fairly complex configuration). However Firefox changed it’s treatment of applets recently which caused a problem with the image upload applet which is discussed in this thread: XNAT 1.7 problem uploading images JAVA plugin is not support.
The vagrant-dpuk-node project which is the reference install for a dpuk node now includes a module that fixes the upload applet problem, at least temporarily, until a more long term solution is implemented for xnat.