diff --git a/mozilla/docshell/base/nsDocShell.cpp b/mozilla/docshell/base/nsDocShell.cpp
index 0ebf93a516a..7e89fddb437 100644
--- a/mozilla/docshell/base/nsDocShell.cpp
+++ b/mozilla/docshell/base/nsDocShell.cpp
@@ -2003,4 +2003,7 @@ nsresult nsDocShell::GetPrimaryFrameFor(nsIContent* content, nsIFrame** frame)
    return NS_ERROR_FAILURE;
 }
 
-
+NS_IMETHODIMP nsDocShell::QueryCapability(const nsIID& anIID, void** aSink)
+{
+  return QueryInterface(anIID, aSink);
+}
diff --git a/mozilla/docshell/base/nsDocShell.h b/mozilla/docshell/base/nsDocShell.h
index 919dc3c085f..e6a835d54db 100644
--- a/mozilla/docshell/base/nsDocShell.h
+++ b/mozilla/docshell/base/nsDocShell.h
@@ -81,6 +81,7 @@ public:
    NS_DECL_NSISCROLLABLE
    NS_DECL_NSITEXTSCROLL
    NS_DECL_NSIHTMLDOCSHELL
+   NS_DECL_NSICAPABILITIES
 
    // XXX: move to a macro
    // nsIContentViewerContainer