diff --git a/image/decoders/icon/mac/nsIconChannel.h b/image/decoders/icon/mac/nsIconChannel.h
index 2ba6691c26dd..08fbadaf2a4d 100644
--- a/image/decoders/icon/mac/nsIconChannel.h
+++ b/image/decoders/icon/mac/nsIconChannel.h
@@ -40,7 +40,6 @@ protected:
 
   nsCOMPtr<nsIURI> mUrl;
   nsCOMPtr<nsIURI> mOriginalURI;
-  int64_t mContentLength;
   nsCOMPtr<nsILoadGroup> mLoadGroup;
   nsCOMPtr<nsIInterfaceRequestor> mCallbacks;
   nsCOMPtr<nsISupports>  mOwner;
diff --git a/image/decoders/icon/mac/nsIconChannelCocoa.mm b/image/decoders/icon/mac/nsIconChannelCocoa.mm
index 0474ab66d32e..455b0b44a409 100644
--- a/image/decoders/icon/mac/nsIconChannelCocoa.mm
+++ b/image/decoders/icon/mac/nsIconChannelCocoa.mm
@@ -460,8 +460,8 @@ nsIconChannel::
 NS_IMETHODIMP
 nsIconChannel::GetContentLength(int64_t* aContentLength)
 {
-  *aContentLength = mContentLength;
-  return NS_OK;
+  *aContentLength = 0;
+  return NS_ERROR_FAILURE;
 }
 
 NS_IMETHODIMP
diff --git a/image/decoders/icon/win/nsIconChannel.cpp b/image/decoders/icon/win/nsIconChannel.cpp
index 4f1fb717501a..2ed0f685ee54 100644
--- a/image/decoders/icon/win/nsIconChannel.cpp
+++ b/image/decoders/icon/win/nsIconChannel.cpp
@@ -708,8 +708,8 @@ nsIconChannel::
 NS_IMETHODIMP
 nsIconChannel::GetContentLength(int64_t* aContentLength)
 {
-  *aContentLength = mContentLength;
-  return NS_OK;
+  *aContentLength = 0;
+  return NS_ERROR_FAILURE;
 }
 
 NS_IMETHODIMP
diff --git a/image/decoders/icon/win/nsIconChannel.h b/image/decoders/icon/win/nsIconChannel.h
index 9f0d9423fa99..af29ca9bb1b3 100644
--- a/image/decoders/icon/win/nsIconChannel.h
+++ b/image/decoders/icon/win/nsIconChannel.h
@@ -43,7 +43,6 @@ public:
 protected:
   nsCOMPtr<nsIURI> mUrl;
   nsCOMPtr<nsIURI> mOriginalURI;
-  int64_t          mContentLength;
   nsCOMPtr<nsILoadGroup> mLoadGroup;
   nsCOMPtr<nsIInterfaceRequestor> mCallbacks;
   nsCOMPtr<nsISupports>  mOwner;