--- a/dom/events/DataTransfer.cpp
+++ b/dom/events/DataTransfer.cpp
@@ -1298,23 +1298,16 @@ DataTransfer::CacheExternalData(const ch
   item = mItems->SetDataWithPrincipal(format, nullptr, aIndex,
                                       aPrincipal, false, aHidden, rv);
   if (NS_WARN_IF(rv.Failed())) {
     return rv.StealNSResult();
   }
   return NS_OK;
 }
 
-// there isn't a way to get a list of the formats that might be available on
-// all platforms, so just check for the types that can actually be imported
-// XXXndeakin there are some other formats but those are platform specific.
-const char* kFormats[] = { kFileMime, kHTMLMime, kURLMime, kURLDataMime,
-                           kUnicodeMime, kPNGImageMime, kJPEGImageMime,
-                           kGIFImageMime };
-
 void
 DataTransfer::CacheExternalDragFormats()
 {
   // Called during the constructor to cache the formats available from an
   // external drag. The data associated with each format will be set to null.
   // This data will instead only be retrieved in FillInExternalDragData when
   // asked for, as it may be time consuming for the source application to
   // generate it.
@@ -1327,18 +1320,19 @@ DataTransfer::CacheExternalDragFormats()
   // make sure that the system principal is used for external drags
   nsIScriptSecurityManager* ssm = nsContentUtils::GetSecurityManager();
   nsCOMPtr<nsIPrincipal> sysPrincipal;
   ssm->GetSystemPrincipal(getter_AddRefs(sysPrincipal));
 
   // there isn't a way to get a list of the formats that might be available on
   // all platforms, so just check for the types that can actually be imported
   // XXXndeakin there are some other formats but those are platform specific.
-  const char* formats[] = { kFileMime, kHTMLMime, kRTFMime,
-                            kURLMime, kURLDataMime, kUnicodeMime };
+  // NOTE: kFileMime must have index 0
+  const char* formats[] = { kFileMime, kHTMLMime, kURLMime, kURLDataMime,
+                            kUnicodeMime, kPNGImageMime };
 
   uint32_t count;
   dragSession->GetNumDropItems(&count);
   for (uint32_t c = 0; c < count; c++) {
     bool hasFileData = false;
     dragSession->IsDataFlavorSupported(kFileMime, &hasFileData);
 
     // First, check for the special format that holds custom types.
@@ -1349,21 +1343,21 @@ DataTransfer::CacheExternalDragFormats()
     }
 
     for (uint32_t f = 0; f < ArrayLength(formats); f++) {
       // IsDataFlavorSupported doesn't take an index as an argument and just
       // checks if any of the items support a particular flavor, even though
       // the GetData method does take an index. Here, we just assume that
       // every item being dragged has the same set of flavors.
       bool supported;
-      dragSession->IsDataFlavorSupported(kFormats[f], &supported);
+      dragSession->IsDataFlavorSupported(formats[f], &supported);
       // if the format is supported, add an item to the array with null as
       // the data. When retrieved, GetRealData will read the data.
       if (supported) {
-        CacheExternalData(kFormats[f], c, sysPrincipal, /* hidden = */ f && hasFileData);
+        CacheExternalData(formats[f], c, sysPrincipal, /* hidden = */ f && hasFileData);
       }
     }
   }
 }
 
 void
 DataTransfer::CacheExternalClipboardFormats()
 {
@@ -1386,20 +1380,19 @@ DataTransfer::CacheExternalClipboardForm
 
   // Check if the clipboard has any files
   bool hasFileData = false;
   const char *fileMime[] = { kFileMime };
   clipboard->HasDataMatchingFlavors(fileMime, 1, mClipboardType, &hasFileData);
 
   // there isn't a way to get a list of the formats that might be available on
   // all platforms, so just check for the types that can actually be imported.
-  // Note that the loop below assumes that kCustomTypesMime will be first.
+  // NOTE: kCustomTypesMime must have index 0, kFileMime index 1
   const char* formats[] = { kCustomTypesMime, kFileMime, kHTMLMime, kRTFMime,
-                            kURLMime, kURLDataMime, kUnicodeMime, kPNGImageMime,
-                            kJPEGImageMime, kGIFImageMime };
+                            kURLMime, kURLDataMime, kUnicodeMime, kPNGImageMime };
 
   for (uint32_t f = 0; f < mozilla::ArrayLength(formats); ++f) {
     // check each format one at a time
     bool supported;
     clipboard->HasDataMatchingFlavors(&(formats[f]), 1, mClipboardType,
                                       &supported);
     // if the format is supported, add an item to the array with null as
     // the data. When retrieved, GetRealData will read the data.