diff --git a/browser/app/nsBrowserApp.cpp b/browser/app/nsBrowserApp.cpp
index da3b24e90f6..d04b4093056 100644
--- a/browser/app/nsBrowserApp.cpp
+++ b/browser/app/nsBrowserApp.cpp
@@ -45,6 +45,10 @@
 #include <stdio.h>
 #include <stdarg.h>
 
+#include "plstr.h"
+#include "prprf.h"
+#include "prenv.h"
+
 #include "nsCOMPtr.h"
 #include "nsILocalFile.h"
 #include "nsStringGlue.h"
@@ -67,8 +71,40 @@ static void Output(const char *fmt, ... )
   va_end(ap);
 }
 
+/**
+ * Return true if |arg| matches the given argument name.
+ */
+static PRBool IsArg(const char* arg, const char* s)
+{
+  if (*arg == '-')
+  {
+    if (*++arg == '-')
+      ++arg;
+    return !PL_strcasecmp(arg, s);
+  }
+
+#if defined(XP_WIN) || defined(XP_OS2)
+  if (*arg == '/')
+    return !PL_strcasecmp(++arg, s);
+#endif
+
+  return PR_FALSE;
+}
+
+/**
+ * A helper class which calls NS_LogTerm/NS_LogTerm in its scope.
+ */
+class ScopedLogging
+{
+public:
+  ScopedLogging() { NS_LogInit(); }
+  ~ScopedLogging() { NS_LogTerm(); }
+};
+
 int main(int argc, char* argv[])
 {
+  ScopedLogging log;
+
   nsCOMPtr<nsILocalFile> appini;
   nsresult rv = XRE_GetBinaryPath(argv[0], getter_AddRefs(appini));
   if (NS_FAILED(rv)) {
@@ -77,6 +113,36 @@ int main(int argc, char* argv[])
   }
   appini->SetNativeLeafName(NS_LITERAL_CSTRING("application.ini"));
 
+  // Allow firefox.exe to launch XULRunner apps via -app <application.ini>
+  // Note that -app must be the *first* argument.
+  char *appEnv = nsnull;
+  const char *appDataFile = PR_GetEnv("XUL_APP_FILE");
+  if (appDataFile && *appDataFile) {
+    rv = XRE_GetFileFromPath(appDataFile, getter_AddRefs(appini));
+    if (NS_FAILED(rv)) {
+      Output("Invalid path found: '%s'", appDataFile);
+      return 255;
+    }
+  }
+  else if (argc > 1 && IsArg(argv[1], "app")) {
+    if (argc == 2) {
+      Output("Incorrect number of arguments passed to -app");
+      return 255;
+    }
+
+    rv = XRE_GetFileFromPath(argv[2], getter_AddRefs(appini));
+    if (NS_FAILED(rv)) {
+      Output("application.ini path not recognized: '%s'", argv[2]);
+      return 255;
+    }
+
+    appEnv = PR_smprintf("XUL_APP_FILE=%s", argv[2]);
+    PR_SetEnv(appEnv);
+    argv[2] = argv[0];
+    argv += 2;
+    argc -= 2;
+  }
+
   nsXREAppData *appData;
   rv = XRE_CreateAppData(appini, &appData);
   if (NS_FAILED(rv)) {
@@ -86,6 +152,8 @@ int main(int argc, char* argv[])
 
   int result = XRE_main(argc, argv, appData);
   XRE_FreeAppData(appData);
+  if (appEnv)
+    PR_smprintf_free(appEnv);
   return result;
 }
 
diff --git a/toolkit/xre/nsAppData.cpp b/toolkit/xre/nsAppData.cpp
index 492b705ae42..2c33516e8dc 100644
--- a/toolkit/xre/nsAppData.cpp
+++ b/toolkit/xre/nsAppData.cpp
@@ -40,6 +40,7 @@
 #include "nsILocalFile.h"
 #include "nsAppRunner.h"
 #include "nsCRTGlue.h"
+#include "nsAutoPtr.h"
 
 void
 SetAllocatedString(const char *&str, const char *newvalue)
@@ -114,19 +115,27 @@ XRE_CreateAppData(nsILocalFile* aINIFile, nsXREAppData **aAppData)
 {
   NS_ENSURE_ARG(aINIFile && aAppData);
 
-  nsXREAppData *data = new ScopedAppData();
+  nsAutoPtr<nsXREAppData> data = new ScopedAppData();
   if (!data)
     return NS_ERROR_OUT_OF_MEMORY;
 
   nsresult rv = XRE_ParseAppData(aINIFile, data);
-  if (NS_FAILED(rv)) {
-    delete data;
-  }
-  else {
-    *aAppData = data;
+  if (NS_FAILED(rv))
+    return rv;
+
+  if (!data->directory) {
+    nsCOMPtr<nsIFile> appDir;
+    rv = aINIFile->GetParent(getter_AddRefs(appDir));
+    if (NS_FAILED(rv))
+      return rv;
+
+    rv = CallQueryInterface(appDir, &data->directory);
+    if (NS_FAILED(rv))
+      return rv;
   }
 
-  return rv;
+  *aAppData = data.forget();
+  return NS_OK;
 }
 
 struct ReadString {
diff --git a/xulrunner/app/nsXULRunnerApp.cpp b/xulrunner/app/nsXULRunnerApp.cpp
index 9669793d9c5..f4eb4aab9b8 100644
--- a/xulrunner/app/nsXULRunnerApp.cpp
+++ b/xulrunner/app/nsXULRunnerApp.cpp
@@ -443,17 +443,6 @@ int main(int argc, char* argv[])
     return 2;
   }
 
-  if (!appData->directory) {
-    nsCOMPtr<nsIFile> appDir;
-    rv = appDataLF->GetParent(getter_AddRefs(appDir));
-    if (NS_FAILED(rv)) {
-      Output(PR_TRUE, "Error: could not get application directory.\n");
-      return 2;
-    }
-
-    CallQueryInterface(appDir, &appData->directory);
-  }
-
   return XRE_main(argc, argv, appData);
 }