diff --git a/layout/base/nsIPresShell.h b/layout/base/nsIPresShell.h
index 37bd6224c857..b84c65f7f49f 100644
--- a/layout/base/nsIPresShell.h
+++ b/layout/base/nsIPresShell.h
@@ -33,6 +33,8 @@ class nsIDeviceContext;
 class nsIRenderingContext;
 class nsIPageSequenceFrame;
 class nsISelection;
+class nsString;
+class nsStringArray;
 
 #define NS_IPRESSHELL_IID     \
 { 0x76e79c60, 0x944e, 0x11d1, \
@@ -64,6 +66,15 @@ public:
 
   virtual nsIStyleSet* GetStyleSet() = 0;
 
+  NS_IMETHOD GetActiveAlternateStyleSheet(nsString& aSheetTitle) = 0;
+  NS_IMETHOD SelectAlternateStyleSheet(const nsString& aSheetTitle) = 0;
+
+  /**
+   * Gather titles of all selectable (alternate and preferred) style sheets
+   * fills void array with nsString* caller must free strings
+   */
+  NS_IMETHOD ListAlternateStyleSheets(nsStringArray& aTitleList) = 0;
+
   /** GetSelection will return the selection that the presentation shell may implement.
    *  @param aSelection will hold the return value
    */
diff --git a/layout/base/public/nsIPresShell.h b/layout/base/public/nsIPresShell.h
index 37bd6224c857..b84c65f7f49f 100644
--- a/layout/base/public/nsIPresShell.h
+++ b/layout/base/public/nsIPresShell.h
@@ -33,6 +33,8 @@ class nsIDeviceContext;
 class nsIRenderingContext;
 class nsIPageSequenceFrame;
 class nsISelection;
+class nsString;
+class nsStringArray;
 
 #define NS_IPRESSHELL_IID     \
 { 0x76e79c60, 0x944e, 0x11d1, \
@@ -64,6 +66,15 @@ public:
 
   virtual nsIStyleSet* GetStyleSet() = 0;
 
+  NS_IMETHOD GetActiveAlternateStyleSheet(nsString& aSheetTitle) = 0;
+  NS_IMETHOD SelectAlternateStyleSheet(const nsString& aSheetTitle) = 0;
+
+  /**
+   * Gather titles of all selectable (alternate and preferred) style sheets
+   * fills void array with nsString* caller must free strings
+   */
+  NS_IMETHOD ListAlternateStyleSheets(nsStringArray& aTitleList) = 0;
+
   /** GetSelection will return the selection that the presentation shell may implement.
    *  @param aSelection will hold the return value
    */