Index: trunk/src/org/openstreetmap/josm/tools/HttpClient.java
===================================================================
--- trunk/src/org/openstreetmap/josm/tools/HttpClient.java	(revision 15967)
+++ trunk/src/org/openstreetmap/josm/tools/HttpClient.java	(revision 15968)
@@ -535,5 +535,7 @@
      */
     public static HttpClient create(URL url, String requestMethod) {
-        return factory.create(url, requestMethod);
+        return factory.create(url, requestMethod)
+                // #18812: specify `Accept=*/*` to prevent Java from adding `Accept=text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2`
+                .setAccept("*/*");
     }