diff --git a/extensions/layout-debug/src/Makefile.in b/extensions/layout-debug/src/Makefile.in
index ed141cbbd5d..17044d833c5 100644
--- a/extensions/layout-debug/src/Makefile.in
+++ b/extensions/layout-debug/src/Makefile.in
@@ -63,6 +63,7 @@ REQUIRES	= xpcom \
 		  pref \
 		  appshell \
 		  appcomps \
+		  toolkitcomps \
 		  $(NULL)
 
 XPIDLSRCS	= \
diff --git a/extensions/layout-debug/src/nsDebugFactory.cpp b/extensions/layout-debug/src/nsDebugFactory.cpp
index bf65802da3f..8410871a52a 100644
--- a/extensions/layout-debug/src/nsDebugFactory.cpp
+++ b/extensions/layout-debug/src/nsDebugFactory.cpp
@@ -43,11 +43,49 @@
 #include "nsLayoutDebuggingTools.h"
 #include "nsLayoutDebugCLH.h"
 #include "nsIGenericFactory.h"
+#include "nsICategoryManager.h"
+#include "nsIServiceManager.h"
 
 NS_GENERIC_FACTORY_CONSTRUCTOR(nsRegressionTester)
 NS_GENERIC_FACTORY_CONSTRUCTOR(nsLayoutDebuggingTools)
 NS_GENERIC_FACTORY_CONSTRUCTOR(nsLayoutDebugCLH)
 
+#ifdef MOZ_XUL_APP
+
+static NS_IMETHODIMP
+RegisterCommandLineHandlers(nsIComponentManager* compMgr, nsIFile* path,
+                            const char *location, const char *type,
+                            const nsModuleComponentInfo *info)
+{
+  nsresult rv;
+  nsCOMPtr<nsICategoryManager> catMan (do_GetService(NS_CATEGORYMANAGER_CONTRACTID));
+  NS_ENSURE_TRUE(catMan, NS_ERROR_FAILURE);
+
+  rv = catMan->AddCategoryEntry("command-line-handler", "m-layoutdebug",
+                                "@mozilla.org/commandlinehandler/general-startup;1?type=layoutdebug",
+                                PR_TRUE, PR_TRUE, nsnull);
+  if (NS_FAILED(rv))
+    return NS_ERROR_FAILURE;
+
+  return NS_OK;
+}
+
+static NS_IMETHODIMP
+UnregisterCommandLineHandlers(nsIComponentManager* compMgr, nsIFile *path,
+                              const char *location,
+                              const nsModuleComponentInfo *info)
+{
+  nsCOMPtr<nsICategoryManager> catMan (do_GetService(NS_CATEGORYMANAGER_CONTRACTID));
+  NS_ENSURE_TRUE(catMan, NS_ERROR_FAILURE);
+
+  catMan->DeleteCategoryEntry("command-line-handler", "m-layoutdebug",
+                              PR_TRUE);
+
+  return NS_OK;
+}
+
+#endif
+
 static const nsModuleComponentInfo components[] =
 {
   { "nsRegressionTester",
@@ -64,8 +102,13 @@ static const nsModuleComponentInfo components[] =
     NS_LAYOUTDEBUGCLH_CID,
     "@mozilla.org/commandlinehandler/general-startup;1?type=layoutdebug",
     nsLayoutDebugCLHConstructor,
+#ifdef MOZ_XUL_APP
+    RegisterCommandLineHandlers,
+    UnregisterCommandLineHandlers
+#else
     nsLayoutDebugCLH::RegisterProc,
     nsLayoutDebugCLH::UnregisterProc
+#endif
   }
 };
 
diff --git a/extensions/layout-debug/src/nsLayoutDebugCLH.cpp b/extensions/layout-debug/src/nsLayoutDebugCLH.cpp
index 5704cff2cc8..9d33b816e8e 100644
--- a/extensions/layout-debug/src/nsLayoutDebugCLH.cpp
+++ b/extensions/layout-debug/src/nsLayoutDebugCLH.cpp
@@ -40,6 +40,14 @@
 #include "nsLayoutDebugCLH.h"
 #include "nsString.h"
 #include "plstr.h"
+#include "nsCOMPtr.h"
+#include "nsIWindowWatcher.h"
+#include "nsIServiceManager.h"
+#include "nsIDOMWindow.h"
+
+#ifdef MOZ_XUL_APP
+#include "nsICommandLine.h"
+#endif
 
 nsLayoutDebugCLH::nsLayoutDebugCLH()
 {
@@ -49,7 +57,41 @@ nsLayoutDebugCLH::~nsLayoutDebugCLH()
 {
 }
 
-NS_IMPL_ISUPPORTS1(nsLayoutDebugCLH, nsICmdLineHandler)
+NS_IMPL_ISUPPORTS1(nsLayoutDebugCLH, ICOMMANDLINEHANDLER)
+
+#ifdef MOZ_XUL_APP
+
+NS_IMETHODIMP
+nsLayoutDebugCLH::Handle(nsICommandLine* aCmdLine)
+{
+    nsresult rv;
+    PRBool found;
+
+    rv = aCmdLine->HandleFlag(NS_LITERAL_STRING("layoutdebug"),
+                              PR_FALSE, &found);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    nsCOMPtr<nsIWindowWatcher> wwatch (do_GetService(NS_WINDOWWATCHER_CONTRACTID));
+    NS_ENSURE_TRUE(wwatch, NS_ERROR_FAILURE);
+
+    nsCOMPtr<nsIDOMWindow> opened;
+    // XXX passing |aCmdLine| here to work around inconsistent
+    // window watcher behavior (see bug 277798)
+    wwatch->OpenWindow(nsnull, "chrome://layoutdebug/content/",
+                       "_blank", "chrome,dialog=no,all", aCmdLine,
+                       getter_AddRefs(opened));
+    aCmdLine->SetPreventDefault(PR_TRUE);
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLayoutDebugCLH::GetHelpInfo(nsACString& aResult)
+{
+    aResult.Assign(NS_LITERAL_CSTRING("  -layoutdebug         Start with Layout Debugger\n"));
+    return NS_OK;
+}
+
+#else // !MOZ_XUL_APP
 
 CMDLINEHANDLER_IMPL(nsLayoutDebugCLH, "-layoutdebug",
                     "general.startup.layoutdebug",
@@ -60,3 +102,5 @@ CMDLINEHANDLER_IMPL(nsLayoutDebugCLH, "-layoutdebug",
                     PR_TRUE,
                     "",
                     PR_TRUE)
+
+#endif
diff --git a/extensions/layout-debug/src/nsLayoutDebugCLH.h b/extensions/layout-debug/src/nsLayoutDebugCLH.h
index f76d6e6d8b2..253b748c282 100644
--- a/extensions/layout-debug/src/nsLayoutDebugCLH.h
+++ b/extensions/layout-debug/src/nsLayoutDebugCLH.h
@@ -40,21 +40,31 @@
 #ifndef nsLayoutDebugCLH_h_
 #define nsLayoutDebugCLH_h_
 
+#ifdef MOZ_XUL_APP
+#include "nsICommandLineHandler.h"
+#define ICOMMANDLINEHANDLER nsICommandLineHandler
+#else
 #include "nsICmdLineHandler.h"
+#define ICOMMANDLINEHANDLER nsICmdLineHandler
+#endif
 
 #define NS_LAYOUTDEBUGCLH_CID \
  { 0xa8f52633, 0x5ecf, 0x424a, \
    { 0xa1, 0x47, 0x47, 0xc3, 0x22, 0xf7, 0xbc, 0xe2 }}
 
-class nsLayoutDebugCLH : public nsICmdLineHandler
+class nsLayoutDebugCLH : public ICOMMANDLINEHANDLER
 {
 public:
     nsLayoutDebugCLH();
     virtual ~nsLayoutDebugCLH();
 
     NS_DECL_ISUPPORTS
+#ifdef MOZ_XUL_APP
+    NS_DECL_NSICOMMANDLINEHANDLER
+#else
     NS_DECL_NSICMDLINEHANDLER
     CMDLINEHANDLER_REGISTERPROC_DECLS
+#endif
 };
 
 #endif /* !defined(nsLayoutDebugCLH_h_) */