--- a/content/canvas/src/WebGLElementArrayCache.cpp
+++ b/content/canvas/src/WebGLElementArrayCache.cpp
@@ -328,16 +328,19 @@ struct TreeForType<uint16_t>
 };
 
 // When the buffer gets updated from firstByte to lastByte,
 // calling this method will notify the tree accordingly
 template<typename T>
 void WebGLElementArrayCacheTree<T>::Invalidate(size_t firstByte, size_t lastByte)
 {
   lastByte = NS_MIN(lastByte, mNumLeaves * sElementsPerLeaf * sizeof(T) - 1);
+  if (firstByte > lastByte) {
+    return;
+  }
 
   size_t firstLeaf = LeafForByte(firstByte);
   size_t lastLeaf = LeafForByte(lastByte);
 
   if (mInvalidated) {
     mFirstInvalidatedLeaf = NS_MIN(firstLeaf, mFirstInvalidatedLeaf);
     mLastInvalidatedLeaf = NS_MAX(lastLeaf, mLastInvalidatedLeaf);
   } else {