--- a/dom/performance/PerformanceNavigationTiming.cpp
+++ b/dom/performance/PerformanceNavigationTiming.cpp
@@ -78,17 +78,18 @@ PerformanceNavigationTiming::Type()
       break;
     case nsDOMNavigationTiming::TYPE_RELOAD:
       return NavigationType::Reload;
       break;
     case nsDOMNavigationTiming::TYPE_BACK_FORWARD:
       return NavigationType::Back_forward;
       break;
     default:
-      MOZ_CRASH(); // Should not happen
+      // The type is TYPE_RESERVED or some other value that was later added.
+      // We fallback to the default of Navigate.
       return NavigationType::Navigate;
   }
 }
 
 uint16_t
 PerformanceNavigationTiming::RedirectCount()
 {
   return mTiming->GetRedirectCount();