diff -r 000000000000 -r 6474c204b198 toolkit/xre/nsConsoleWriter.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/xre/nsConsoleWriter.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,95 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsAppRunner.h"
+
+#include "prio.h"
+#include "prprf.h"
+#include "prenv.h"
+
+#include "nsCRT.h"
+#include "nsNativeCharsetUtils.h"
+#include "nsString.h"
+#include "nsXREDirProvider.h"
+#include "nsXULAppAPI.h"
+
+#include "nsIConsoleService.h"
+#include "nsIConsoleMessage.h"
+
+void
+WriteConsoleLog()
+{
+  nsresult rv;
+
+  nsCOMPtr<nsIFile> lfile;
+
+  char* logFileEnv = PR_GetEnv("XRE_CONSOLE_LOG");
+  if (logFileEnv && *logFileEnv) {
+    rv = XRE_GetFileFromPath(logFileEnv, getter_AddRefs(lfile));
+    if (NS_FAILED(rv))
+      return;
+  }
+  else {
+    if (!gLogConsoleErrors)
+      return;
+
+    rv = gDirServiceProvider->GetUserAppDataDirectory(getter_AddRefs(lfile));
+    if (NS_FAILED(rv))
+      return;
+
+    lfile->AppendNative(NS_LITERAL_CSTRING("console.log"));
+  }
+
+  PRFileDesc *file;
+  rv = lfile->OpenNSPRFileDesc(PR_WRONLY | PR_APPEND | PR_CREATE_FILE,
+                               0660, &file);
+  if (NS_FAILED(rv))
+    return;
+
+  nsCOMPtr<nsIConsoleService> csrv
+    (do_GetService(NS_CONSOLESERVICE_CONTRACTID));
+  if (!csrv) {
+    PR_Close(file);
+    return;
+  }
+
+  nsIConsoleMessage** messages;
+  uint32_t mcount;
+
+  rv = csrv->GetMessageArray(&mcount, &messages);
+  if (NS_FAILED(rv)) {
+    PR_Close(file);
+    return;
+  }
+
+  if (mcount) {
+    PRExplodedTime etime;
+    PR_ExplodeTime(PR_Now(), PR_LocalTimeParameters, &etime);
+    char datetime[512];
+    PR_FormatTimeUSEnglish(datetime, sizeof(datetime),
+                           "%Y-%m-%d %H:%M:%S", &etime);
+
+    PR_fprintf(file, NS_LINEBREAK
+                     "*** Console log: %s ***" NS_LINEBREAK,
+               datetime);
+  }
+
+  // From this point on, we have to release all the messages, and free
+  // the memory allocated for the messages array. XPCOM arrays suck.
+
+  nsXPIDLString msg;
+  nsAutoCString nativemsg;
+
+  for (uint32_t i = 0; i < mcount; ++i) {
+    rv = messages[i]->GetMessageMoz(getter_Copies(msg));
+    if (NS_SUCCEEDED(rv)) {
+      NS_CopyUnicodeToNative(msg, nativemsg);
+      PR_fprintf(file, "%s" NS_LINEBREAK, nativemsg.get());
+    }
+    NS_IF_RELEASE(messages[i]);
+  }
+
+  PR_Close(file);
+  NS_Free(messages);
+}