--- a/mfbt/RollingMean.h
+++ b/mfbt/RollingMean.h
@@ -81,17 +81,17 @@ public:
   }
 
   /**
    * Calculate the rolling mean.
    */
   T mean()
   {
     MOZ_ASSERT(!empty());
-    return T(mTotal / mValues.length());
+    return T(mTotal / int64_t(mValues.length()));
   }
 
   bool empty()
   {
     return mValues.empty();
   }
 
   /**

--- a/xpcom/ds/TimeStamp.h
+++ b/xpcom/ds/TimeStamp.h
@@ -176,16 +176,21 @@ public:
     return FromTicks(ticks);
   }
 
 private:
   // Block double multiplier (slower, imprecise if long duration) - Bug 853398.
   // If required, use MultDouble explicitly and with care.
   BaseTimeDuration operator*(const double aMultiplier) const = delete;
 
+  // Block double divisor (for the same reason, and because dividing by
+  // fractional values would otherwise invoke the int64_t variant, and rounding
+  // the passed argument can then cause divide-by-zero) - Bug 1147491.
+  BaseTimeDuration operator/(const double aDivisor) const = delete;
+
 public:
   BaseTimeDuration MultDouble(double aMultiplier) const
   {
     return FromTicks(ValueCalculator::Multiply(mValue, aMultiplier));
   }
   BaseTimeDuration operator*(const int32_t aMultiplier) const
   {
     return FromTicks(ValueCalculator::Multiply(mValue, aMultiplier));