--- core/src/org/netbeans/core/LookupCache.java	
+++ core/src/org/netbeans/core/LookupCache.java	
@@ -263,11 +263,18 @@ 
 
                                                            if (bangSlash != -1) {
                                                                // underlying URL inside jar:, generally file:
+                                                               // XXX why is this not using FileUtil.getArchiveFile?
                                                                try {
                                                                    URI layerJarURL = new URI(s.substring(4,
                                                                                                          bangSlash));
 
                                                                    if ("file".equals(layerJarURL.getScheme())) {
+                                                                       { // #121777
+                                                                           String s2 = layerJarURL.toString();
+                                                                           if (s2.startsWith("file:") && !s2.startsWith("file:/")) {
+                                                                               layerJarURL = new URI("file:/" + s2.substring(5));
+                                                                           }
+                                                                       }
                                                                        files.add(new File(layerJarURL));
                                                                    } else {
                                                                        err.warning(
--- core/startup/src/org/netbeans/core/startup/ModuleSystem.java	
+++ core/startup/src/org/netbeans/core/startup/ModuleSystem.java	
@@ -196,14 +196,18 @@ 
                     continue;
                 }
                 URL jarURL = FileUtil.getArchiveFile(manifestUrl);
+                if (jarURL != null && jarURL.getProtocol().equals("file") &&
+                        /* #121777 */ jarURL.getPath().startsWith("/")) {
+                    LOG.log(Level.FINE, "Considering JAR: {0}", jarURL);
                 try {
-                    if (jarURL != null && jarURL.getProtocol().equals("file") && ignoredJars.contains(new File(jarURL.toURI()))) {
+                        if (ignoredJars.contains(new File(jarURL.toURI()))) {
                         LOG.log(Level.FINE, "ignoring JDK/JRE manifest: {0}", manifestUrl);
                         continue MANIFESTS;
                     }
                 } catch (URISyntaxException x) {
                     Exceptions.printStackTrace(x);
                 }
+                }
                 LOG.log(Level.FINE, "Checking boot manifest: {0}", manifestUrl);
                 
                 InputStream is;