diff --git a/modules/libmar/src/mar.h b/modules/libmar/src/mar.h
index aa717eef174..45f46e835a7 100644
--- a/modules/libmar/src/mar.h
+++ b/modules/libmar/src/mar.h
@@ -76,6 +76,10 @@ typedef int (* MarItemCallback)(MarFile *mar, const MarItem *item, void *data);
  */
 MarFile *mar_open(const char *path);
 
+#ifdef XP_WIN
+MarFile *mar_wopen(const PRUnichar *path);
+#endif
+
 /**
  * Close a MAR file that was opened using mar_open.
  * @param mar       The MarFile object to close.
diff --git a/modules/libmar/src/mar_read.c b/modules/libmar/src/mar_read.c
index 8ae3a771da4..b8468c2d13c 100644
--- a/modules/libmar/src/mar_read.c
+++ b/modules/libmar/src/mar_read.c
@@ -179,13 +179,13 @@ static int mar_read_index(MarFile *mar) {
   return (bufptr == bufend) ? 0 : -1;
 }
 
-MarFile *mar_open(const char *path) {
+/**
+ * Internal shared code for mar_open and mar_wopen.
+ * On failure, will fclose(fp).
+ */
+static MarFile *mar_fpopen(FILE *fp)
+{
   MarFile *mar;
-  FILE *fp;
-
-  fp = fopen(path, "rb");
-  if (!fp)
-    return NULL;
 
   mar = (MarFile *) malloc(sizeof(*mar));
   if (!mar) {
@@ -203,6 +203,28 @@ MarFile *mar_open(const char *path) {
   return mar;
 }
 
+MarFile *mar_open(const char *path) {
+  FILE *fp;
+
+  fp = fopen(path, "rb");
+  if (!fp)
+    return NULL;
+
+  return mar_fpopen(fp);
+}
+
+#ifdef XP_WIN
+MarFile *mar_wopen(const PRUnichar *path) {
+  FILE *fp;
+
+  fp = _wfopen(path, L"rb");
+  if (!fp)
+    return NULL;
+
+  return mar_fpopen(fp);
+}
+#endif
+
 void mar_close(MarFile *mar) {
   MarItem *item;
   int i;
diff --git a/toolkit/mozapps/update/src/updater/archivereader.cpp b/toolkit/mozapps/update/src/updater/archivereader.cpp
index 47f9390ff65..e17e0446720 100644
--- a/toolkit/mozapps/update/src/updater/archivereader.cpp
+++ b/toolkit/mozapps/update/src/updater/archivereader.cpp
@@ -49,12 +49,20 @@
 #endif
 
 int
+#ifdef XP_WIN
+ArchiveReader::Open(const WCHAR *path)
+#else
 ArchiveReader::Open(const char *path)
+#endif
 {
   if (mArchive)
     Close();
 
+#ifdef XP_WIN
+  mArchive = mar_wopen(path);
+#else
   mArchive = mar_open(path);
+#endif
   if (!mArchive)
     return READ_ERROR;
 
diff --git a/toolkit/mozapps/update/src/updater/archivereader.h b/toolkit/mozapps/update/src/updater/archivereader.h
index 05ab38dce5f..2421faedee9 100644
--- a/toolkit/mozapps/update/src/updater/archivereader.h
+++ b/toolkit/mozapps/update/src/updater/archivereader.h
@@ -49,7 +49,12 @@ public:
   ArchiveReader() : mArchive(NULL) {}
   ~ArchiveReader() { Close(); }
 
+#ifdef XP_WIN
+  int Open(const WCHAR *path);
+#else
   int Open(const char *path);
+#endif
+
   void Close();
 
   int ExtractFile(const char *item, const char *destination);
diff --git a/toolkit/mozapps/update/src/updater/updater.cpp b/toolkit/mozapps/update/src/updater/updater.cpp
index 530e2ba24dd..52027c9d0cc 100644
--- a/toolkit/mozapps/update/src/updater/updater.cpp
+++ b/toolkit/mozapps/update/src/updater/updater.cpp
@@ -1127,10 +1127,10 @@ WriteStatusFile(int status)
 {
   // This is how we communicate our completion status to the main application.
 
-  char filename[MAXPATHLEN];
-  snprintf(filename, MAXPATHLEN, "%s/update.status", gSourcePath);
+  NS_tchar filename[MAXPATHLEN];
+  NS_tsnprintf(filename, MAXPATHLEN, NS_T("%s/update.status"), gSourcePath);
 
-  AutoFD fd = ensure_open(filename, O_WRONLY | O_TRUNC | O_CREAT | _O_BINARY, 0644);
+  AutoFD fd = NS_topen(filename, O_WRONLY | O_TRUNC | O_CREAT | _O_BINARY, 0644);
   if (fd < 0)
     return;
 
@@ -1151,8 +1151,8 @@ UpdateThreadFunc(void *param)
 {
   // open ZIP archive and process...
 
-  char dataFile[MAXPATHLEN];
-  snprintf(dataFile, MAXPATHLEN, "%s/update.mar", gSourcePath);
+  NS_tchar dataFile[MAXPATHLEN];
+  NS_tsnprintf(dataFile, MAXPATHLEN, NS_T("%s/update.mar"), gSourcePath);
 
   int rv = gArchiveReader.Open(dataFile);
   if (rv == OK) {