--- a/image/imgLoader.cpp
+++ b/image/imgLoader.cpp
@@ -3,16 +3,17 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "mozilla/Attributes.h"
 #include "mozilla/ClearOnShutdown.h"
 #include "mozilla/Move.h"
 #include "mozilla/Preferences.h"
+ #include "mozilla/ChaosMode.h"
 
 #include "ImageLogging.h"
 #include "nsPrintfCString.h"
 #include "imgLoader.h"
 #include "imgRequestProxy.h"
 
 #include "nsCOMPtr.h"
 
@@ -1767,16 +1768,22 @@ imgLoader::ValidateEntry(imgCacheEntry* 
   void *key = (void*) aCX;
   if (request->LoadId() != key) {
     // If we would need to revalidate this entry, but we're being told to
     // bypass the cache, we don't allow this entry to be used.
     if (aLoadFlags & nsIRequest::LOAD_BYPASS_CACHE) {
       return false;
     }
 
+    if (MOZ_UNLIKELY(ChaosMode::isActive(ChaosFeature::ImageCache))) {
+      if (ChaosMode::randomUint32LessThan(4) < 1) {
+        return false;
+      }
+    }
+
     // Determine whether the cache aEntry must be revalidated...
     validateRequest = ShouldRevalidateEntry(aEntry, aLoadFlags, hasExpired);
 
     MOZ_LOG(gImgLog, LogLevel::Debug,
            ("imgLoader::ValidateEntry validating cache entry. "
             "validateRequest = %d", validateRequest));
   } else if (!key && MOZ_LOG_TEST(gImgLog, LogLevel::Debug)) {
     nsAutoCString spec;

--- a/mfbt/ChaosMode.h
+++ b/mfbt/ChaosMode.h
@@ -22,16 +22,18 @@ enum ChaosFeature {
   // Altering network request scheduling.
   NetworkScheduling = 0x2,
   // Altering timer scheduling.
   TimerScheduling = 0x4,
   // Read and write less-than-requested amounts.
   IOAmounts = 0x8,
   // Iterate over hash tables in random order.
   HashTableIteration = 0x10,
+  // Randomly refuse to use cached version of image (when allowed by spec).
+  ImageCache = 0x20,
   Any = 0xffffffff,
 };
 
 namespace detail {
 extern MFBT_DATA Atomic<uint32_t> gChaosModeCounter;
 extern MFBT_DATA ChaosFeature gChaosFeatures;
 } // namespace detail