--- a/dom/base/nsWindowSizes.h
+++ b/dom/base/nsWindowSizes.h
@@ -14,17 +14,22 @@
 class nsTabSizes {
 public:
   enum Kind {
       DOM,        // DOM stuff.
       Style,      // Style stuff.
       Other       // Everything else.
   };
 
-  nsTabSizes() { mozilla::PodZero(this); }
+  nsTabSizes()
+    : mDom(0)
+    , mStyle(0)
+    , mOther(0)
+  {
+  }
 
   void add(Kind kind, size_t n)
   {
     switch (kind) {
       case DOM:   mDom   += n; break;
       case Style: mStyle += n; break;
       case Other: mOther += n; break;
       default:    MOZ_CRASH("bad nsTabSizes kind");