As a workaround, we uploaded a custom spinner on a secure web server and put the following in our CSS for our Xwiki theme:
.jstree-xwiki>.jstree-container-ul .jstree-loading>.jstree-ocl {
background-image: url(“Free classifieds - yourdomain.com”);
background-size: 23px;
position: relative;
top: -2px;
}
