diff --git a/modules/plugin/test/mochitest/Makefile.in b/modules/plugin/test/mochitest/Makefile.in
index 4c11e61d5f1..b3caba2fa27 100644
--- a/modules/plugin/test/mochitest/Makefile.in
+++ b/modules/plugin/test/mochitest/Makefile.in
@@ -80,6 +80,7 @@ ifdef MOZ_IPC
 _MOCHITEST_FILES += \
   test_crashing.html \
   test_crashing2.html \
+  test_hanging.html \
   crashing_subpage.html \
   $(NULL)
 endif
diff --git a/modules/plugin/test/mochitest/test_hanging.html b/modules/plugin/test/mochitest/test_hanging.html
new file mode 100644
index 00000000000..d9fcc45366d
--- /dev/null
+++ b/modules/plugin/test/mochitest/test_hanging.html
@@ -0,0 +1,75 @@
+<head>
+  <title>Plugin hanging</title>
+  <script type="application/javascript" src="chrome://mochikit/content/MochiKit/packed.js"></script>
+  <script type="application/javascript" src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+
+<body>
+  <iframe id="iframe1" src="crashing_subpage.html" width="600" height="600"></iframe>
+
+  <script class="testbody" type="application/javascript">
+  SimpleTest.waitForExplicitFinish();
+
+  var iframe = document.getElementById('iframe1');
+
+  window.frameLoaded = function frameLoaded_toCrash() {
+    netscape.security.PrivilegeManager.enablePrivilege('UniversalXPConnect');
+    var prefs = Components.classes['@mozilla.org/preferences-service;1']
+      .getService(Components.interfaces.nsIPrefBranch);
+    if (!prefs.getBoolPref('dom.ipc.plugins.enabled')) {
+      ok(true, "Skipping this test when IPC plugins are not enabled.");
+      SimpleTest.finish();
+      return;
+    }
+
+    // the default timeout is annoying high for mochitest runs
+    var timeoutPref = "dom.ipc.plugins.timeoutSecs";
+    prefs.setIntPref(timeoutPref, 5);
+
+    var p = iframe.contentDocument.getElementById('plugin1');
+
+    p.setColor("FFFF00FF");
+
+    try {
+      p.hang();
+      ok(false, "p.hang() should throw an exception");
+    }
+    catch (e) {
+      ok(true, "p.hang() should throw an exception");
+    }
+
+    try {
+      p.setColor("FFFF0000");
+      ok(false, "p.setColor should throw after the plugin crashes");
+    }
+    catch (e) {
+      ok(true, "p.setColor should throw after the plugin crashes");
+    }
+
+    window.frameLoaded = function reloaded() {
+      var p = iframe.contentDocument.getElementById('plugin1');
+      try {
+        p.setColor('FF00FF00');
+        ok(true, "Reloading worked");
+      }
+      catch (e) {
+        ok(false, "Reloading didn't give us a usable plugin");
+      }
+
+      try {
+        netscape.security.PrivilegeManager.enablePrivilege('UniversalXPConnect');
+        var prefs = Components.classes['@mozilla.org/preferences-service;1']
+          .getService(Components.interfaces.nsIPrefBranch);
+
+        prefs.clearUserPref(timeoutPref);
+      }
+      catch(e) {
+        ok(false, "Couldn't reset timeout pref");
+      }
+
+      SimpleTest.finish();
+    }
+
+    iframe.contentWindow.location.reload();
+  }
+
+  </script>
diff --git a/modules/plugin/test/testplugin/nptest.cpp b/modules/plugin/test/testplugin/nptest.cpp
index 0b203c7dac5..747f8f86bc9 100644
--- a/modules/plugin/test/testplugin/nptest.cpp
+++ b/modules/plugin/test/testplugin/nptest.cpp
@@ -67,8 +67,8 @@
 
 int gCrashCount = 0;
 
-void
-IntentionalCrash()
+static void
+NoteIntentionalCrash()
 {
   char* bloatLog = getenv("XPCOM_MEM_BLOAT_LOG");
   if (bloatLog) {
@@ -85,6 +85,13 @@ IntentionalCrash()
     fprintf(processfd, "==> process %d will purposefully crash\n", getpid());
     fclose(processfd);
   }
+}
+
+static void
+IntentionalCrash()
+{
+  NoteIntentionalCrash();
+
   int *pi = NULL;
   *pi = 55; // Crash dereferencing null pointer
   ++gCrashCount;
@@ -146,6 +153,7 @@ static bool getCookie(NPObject* npobj, const NPVariant* args, uint32_t argCount,
 static bool getAuthInfo(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
 static bool asyncCallbackTest(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
 static bool checkGCRace(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
+static bool hangPlugin(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
 
 static const NPUTF8* sPluginMethodIdentifierNames[] = {
   "npnEvaluateTest",
@@ -184,6 +192,7 @@ static const NPUTF8* sPluginMethodIdentifierNames[] = {
   "getAuthInfo",
   "asyncCallbackTest",
   "checkGCRace",
+  "hang",
 };
 static NPIdentifier sPluginMethodIdentifiers[ARRAY_LENGTH(sPluginMethodIdentifierNames)];
 static const ScriptableFunction sPluginMethodFunctions[ARRAY_LENGTH(sPluginMethodIdentifierNames)] = {
@@ -223,6 +232,7 @@ static const ScriptableFunction sPluginMethodFunctions[ARRAY_LENGTH(sPluginMetho
   getAuthInfo,
   asyncCallbackTest,
   checkGCRace,
+  hangPlugin,
 };
 
 struct URLNotifyData
@@ -2552,3 +2562,21 @@ checkGCRace(NPObject* npobj, const NPVariant* args, uint32_t argCount,
   OBJECT_TO_NPVARIANT(localFunc, *result);
   return true;
 }
+
+bool
+hangPlugin(NPObject* npobj, const NPVariant* args, uint32_t argCount,
+           NPVariant* result)
+{
+  NoteIntentionalCrash();
+
+#ifdef XP_WIN
+  Sleep(100000000);
+#else
+  pause();
+#endif
+  // NB: returning true here means that we weren't terminated, and
+  // thus the hang detection/handling didn't work correctly.  The
+  // test harness will succeed in calling this function, and the
+  // test will fail.
+  return true;
+}
