diff --git a/gfx/thebes/gfxDWriteCommon.cpp b/gfx/thebes/gfxDWriteCommon.cpp
index 1852a9c66c42..76d52538f641 100644
--- a/gfx/thebes/gfxDWriteCommon.cpp
+++ b/gfx/thebes/gfxDWriteCommon.cpp
@@ -26,7 +26,8 @@ public:
   *
   * @param aData Font data
   */
-  gfxDWriteFontFileStream(FallibleTArray<uint8_t> *aData,
+  gfxDWriteFontFileStream(const uint8_t* aData,
+                          uint32_t aLength,
                           uint64_t aFontFileKey);
   ~gfxDWriteFontFileStream();
 
@@ -82,11 +83,16 @@ private:
   uint64_t mFontFileKey;
 };
 
-gfxDWriteFontFileStream::gfxDWriteFontFileStream(FallibleTArray<uint8_t> *aData,
+gfxDWriteFontFileStream::gfxDWriteFontFileStream(const uint8_t* aData,
+                                                 uint32_t aLength,
                                                  uint64_t aFontFileKey)
   : mFontFileKey(aFontFileKey)
 {
-  mData.SwapElements(*aData);
+  // If this fails, mData will remain empty. That's OK: GetFileSize()
+  // will then return 0, etc., and the font just won't load.
+  if (!mData.AppendElements(aData, aLength, mozilla::fallible_t())) {
+    NS_WARNING("Failed to store data in gfxDWriteFontFileStream");
+  }
 }
 
 gfxDWriteFontFileStream::~gfxDWriteFontFileStream()
@@ -151,7 +157,8 @@ gfxDWriteFontFileLoader::CreateStreamFromKey(const void *fontFileReferenceKey,
 
 /* static */
 HRESULT
-gfxDWriteFontFileLoader::CreateCustomFontFile(FallibleTArray<uint8_t>& aFontData,
+gfxDWriteFontFileLoader::CreateCustomFontFile(const uint8_t* aFontData,
+                                              uint32_t aLength,
                                               IDWriteFontFile** aFontFile,
                                               IDWriteFontFileStream** aFontFileStream)
 {
@@ -165,7 +172,8 @@ gfxDWriteFontFileLoader::CreateCustomFontFile(FallibleTArray<uint8_t>& aFontData
   }
 
   uint64_t fontFileKey = sNextFontFileKey++;
-  RefPtr<IDWriteFontFileStream> ffsRef = new gfxDWriteFontFileStream(&aFontData, fontFileKey);
+  RefPtr<IDWriteFontFileStream> ffsRef =
+      new gfxDWriteFontFileStream(aFontData, aLength, fontFileKey);
   sFontFileStreams[fontFileKey] = ffsRef;
 
   RefPtr<IDWriteFontFile> fontFile;
diff --git a/gfx/thebes/gfxDWriteCommon.h b/gfx/thebes/gfxDWriteCommon.h
index 65c2df7bcbe4..5bf6a60e0aae 100644
--- a/gfx/thebes/gfxDWriteCommon.h
+++ b/gfx/thebes/gfxDWriteCommon.h
@@ -135,14 +135,17 @@ public:
 
     /**
      * Creates a IDWriteFontFile and IDWriteFontFileStream from aFontData.
-     * aFontData will be empty on return as it swaps out the data.
+     * The data from aFontData will be copied internally, so the caller
+     * is free to dispose of it once this method returns.
      *
      * @param aFontData the font data for the custom font file
+     * @param aLength length of the font data
      * @param aFontFile out param for the created font file
      * @param aFontFileStream out param for the corresponding stream
      * @return HRESULT of internal calls
      */
-    static HRESULT CreateCustomFontFile(FallibleTArray<uint8_t>& aFontData,
+    static HRESULT CreateCustomFontFile(const uint8_t* aFontData,
+                                        uint32_t aLength,
                                         IDWriteFontFile** aFontFile,
                                         IDWriteFontFileStream** aFontFileStream);
 
diff --git a/gfx/thebes/gfxDWriteFontList.cpp b/gfx/thebes/gfxDWriteFontList.cpp
index d3a5f69895f6..e9acbd20bf5a 100644
--- a/gfx/thebes/gfxDWriteFontList.cpp
+++ b/gfx/thebes/gfxDWriteFontList.cpp
@@ -934,41 +934,30 @@ gfxDWriteFontList::MakePlatformFont(const nsAString& aFontName,
                                     const uint8_t* aFontData,
                                     uint32_t aLength)
 {
-    nsresult rv;
-    nsAutoString uniqueName;
-    rv = gfxFontUtils::MakeUniqueUserFontName(uniqueName);
-    if (NS_FAILED(rv)) {
-        free((void*)aFontData);
-        return nullptr;
-    }
-
-    FallibleTArray<uint8_t> newFontData;
-
-    rv = gfxFontUtils::RenameFont(uniqueName, aFontData, aLength, &newFontData);
-    free((void*)aFontData);
-
-    if (NS_FAILED(rv)) {
-        return nullptr;
-    }
-    
     RefPtr<IDWriteFontFileStream> fontFileStream;
     RefPtr<IDWriteFontFile> fontFile;
     HRESULT hr =
-      gfxDWriteFontFileLoader::CreateCustomFontFile(newFontData,
+      gfxDWriteFontFileLoader::CreateCustomFontFile(aFontData, aLength,
                                                     getter_AddRefs(fontFile),
                                                     getter_AddRefs(fontFileStream));
-
+    free((void*)aFontData);
     if (FAILED(hr)) {
         NS_WARNING("Failed to create custom font file reference.");
         return nullptr;
     }
 
+    nsAutoString uniqueName;
+    nsresult rv = gfxFontUtils::MakeUniqueUserFontName(uniqueName);
+    if (NS_FAILED(rv)) {
+        return nullptr;
+    }
+
     BOOL isSupported;
     DWRITE_FONT_FILE_TYPE fileType;
     UINT32 numFaces;
 
     gfxDWriteFontEntry *entry = 
-        new gfxDWriteFontEntry(uniqueName, 
+        new gfxDWriteFontEntry(uniqueName,
                                fontFile,
                                fontFileStream,
                                aWeight,