diff --git a/widget/windows/nsFilePicker.cpp b/widget/windows/nsFilePicker.cpp
index 55daccdcc37b..c110a8f6dabd 100644
--- a/widget/windows/nsFilePicker.cpp
+++ b/widget/windows/nsFilePicker.cpp
@@ -1130,7 +1130,7 @@ nsFilePicker::GetFiles(nsISimpleEnumerator **aFiles)
 
 // Get the file + path
 NS_IMETHODIMP
-nsFilePicker::SetDefaultString(const nsAString& aString)
+nsBaseWinFilePicker::SetDefaultString(const nsAString& aString)
 {
   mDefaultFilePath = aString;
 
@@ -1164,21 +1164,21 @@ nsFilePicker::SetDefaultString(const nsAString& aString)
 }
 
 NS_IMETHODIMP
-nsFilePicker::GetDefaultString(nsAString& aString)
+nsBaseWinFilePicker::GetDefaultString(nsAString& aString)
 {
   return NS_ERROR_FAILURE;
 }
 
 // The default extension to use for files
 NS_IMETHODIMP
-nsFilePicker::GetDefaultExtension(nsAString& aExtension)
+nsBaseWinFilePicker::GetDefaultExtension(nsAString& aExtension)
 {
   aExtension = mDefaultExtension;
   return NS_OK;
 }
 
 NS_IMETHODIMP
-nsFilePicker::SetDefaultExtension(const nsAString& aExtension)
+nsBaseWinFilePicker::SetDefaultExtension(const nsAString& aExtension)
 {
   mDefaultExtension = aExtension;
   return NS_OK;
diff --git a/widget/windows/nsFilePicker.h b/widget/windows/nsFilePicker.h
index 197184b7124f..d2213da422c1 100644
--- a/widget/windows/nsFilePicker.h
+++ b/widget/windows/nsFilePicker.h
@@ -34,13 +34,28 @@
 
 class nsILoadContext;
 
+class nsBaseWinFilePicker :
+  public nsBaseFilePicker
+{
+public:
+  NS_IMETHOD GetDefaultString(nsAString& aDefaultString);
+  NS_IMETHOD SetDefaultString(const nsAString& aDefaultString);
+  NS_IMETHOD GetDefaultExtension(nsAString& aDefaultExtension);
+  NS_IMETHOD SetDefaultExtension(const nsAString& aDefaultExtension);
+
+protected:
+  nsString mDefaultFilePath;
+  nsString mDefaultFilename;
+  nsString mDefaultExtension;
+};
+
 /**
  * Native Windows FileSelector wrapper
  */
 
 class nsFilePicker :
-  public nsBaseFilePicker,
-  public IFileDialogEvents
+  public IFileDialogEvents,
+  public nsBaseWinFilePicker
 {
 public:
   nsFilePicker(); 
@@ -53,11 +68,7 @@ public:
   // IUnknown's QueryInterface
   STDMETHODIMP QueryInterface(REFIID refiid, void** ppvResult);
 
-  // nsIFilePicker (less what's in nsBaseFilePicker)
-  NS_IMETHOD GetDefaultString(nsAString& aDefaultString);
-  NS_IMETHOD SetDefaultString(const nsAString& aDefaultString);
-  NS_IMETHOD GetDefaultExtension(nsAString& aDefaultExtension);
-  NS_IMETHOD SetDefaultExtension(const nsAString& aDefaultExtension);
+  // nsIFilePicker (less what's in nsBaseFilePicker and nsBaseWinFilePicker)
   NS_IMETHOD GetFilterIndex(int32_t *aFilterIndex);
   NS_IMETHOD SetFilterIndex(int32_t aFilterIndex);
   NS_IMETHOD GetFile(nsIFile * *aFile);
@@ -109,9 +120,6 @@ protected:
   nsString               mTitle;
   int16_t                mMode;
   nsCString              mFile;
-  nsString               mDefaultFilePath;
-  nsString               mDefaultFilename;
-  nsString               mDefaultExtension;
   nsString               mFilterList;
   int16_t                mSelectedType;
   nsCOMArray<nsIFile>    mFiles;