--- a/layout/base/RestyleManager.cpp
+++ b/layout/base/RestyleManager.cpp
@@ -3259,17 +3259,17 @@ ElementRestyler::Restyle(nsRestyleHint a
 
   // TEMPORARY (until bug 918064):  Call RestyleSelf for each
   // continuation or block-in-inline sibling.
 
   // We must make a single decision on how to process this frame and
   // its descendants, yet RestyleSelf might return different RestyleResult
   // values for the different same-style continuations.  |result| is our
   // overall decision.
-  RestyleResult result = RestyleResult(0);
+  RestyleResult result = eRestyleResult_None;
   uint32_t swappedStructs = 0;
 
   nsRestyleHint thisRestyleHint = aRestyleHint;
 
   bool haveMoreContinuations = false;
   for (nsIFrame* f = mFrame; f; ) {
     RestyleResult thisResult =
       RestyleSelf(f, thisRestyleHint, &swappedStructs, swaps);
@@ -5189,15 +5189,16 @@ ElementRestyler::RestyleResultToString(R
       break;
     case eRestyleResult_Continue:
       result.AssignLiteral("eRestyleResult_Continue");
       break;
     case eRestyleResult_ContinueAndForceDescendants:
       result.AssignLiteral("eRestyleResult_ContinueAndForceDescendants");
       break;
     default:
-      result.AppendPrintf("RestyleResult(%d)", aRestyleResult);
+      MOZ_ASSERT(aRestyleResult == eRestyleResult_None,
+                 "Unexpected RestyleResult");
   }
   return result;
 }
 #endif
 
 } // namespace mozilla

--- a/layout/base/RestyleManager.h
+++ b/layout/base/RestyleManager.h
@@ -666,19 +666,21 @@ private:
   inline nsStyleSet* StyleSet() const;
 
   // Enum for the result of RestyleSelf, which indicates whether the
   // restyle procedure should continue to the children, and how.
   //
   // These values must be ordered so that later values imply that all
   // the work of the earlier values is also done.
   enum RestyleResult {
+    // default initial value
+    eRestyleResult_None,
 
     // we left the old style context on the frame; do not restyle children
-    eRestyleResult_Stop = 1,
+    eRestyleResult_Stop,
 
     // we got a new style context on this frame, but we know that children
     // do not depend on the changed values; do not restyle children
     eRestyleResult_StopWithStyleChange,
 
     // continue restyling children
     eRestyleResult_Continue,