--- a/dom/workers/test/serviceworkers/fetch/fetch_tests.js
+++ b/dom/workers/test/serviceworkers/fetch/fetch_tests.js
@@ -34,22 +34,16 @@ fetchXHR('test-respondwith-response.txt'
 });
 
 fetchXHR('synthesized-404.txt', function(xhr) {
   my_ok(xhr.status == 404, "load should 404");
   my_ok(xhr.responseText == "synthesized response body", "404 load should have synthesized response");
   finish();
 });
 
-fetchXHR('synthesized-308.txt', function(xhr) {
-  my_ok(xhr.status == 308, "load should return 308");
-  my_ok(xhr.responseText == "synthesized response body", "308 load should have synthesized response");
-  finish();
-});
-
 fetchXHR('synthesized-headers.txt', function(xhr) {
   my_ok(xhr.status == 200, "load should be successful");
   my_ok(xhr.getResponseHeader("X-Custom-Greeting") === "Hello", "custom header should be set");
   my_ok(xhr.responseText == "synthesized response body", "custom header load should have synthesized response");
   finish();
 });
 
 fetchXHR('synthesized-redirect-real-file.txt', function(xhr) {

--- a/dom/workers/test/serviceworkers/fetch_event_worker.js
+++ b/dom/workers/test/serviceworkers/fetch_event_worker.js
@@ -8,22 +8,16 @@ onfetch = function(ev) {
   }
 
   else if (ev.request.url.includes("synthesized-404.txt")) {
     ev.respondWith(Promise.resolve(
       new Response("synthesized response body", { status: 404 })
     ));
   }
 
-  else if (ev.request.url.includes("synthesized-308.txt")) {
-    ev.respondWith(Promise.resolve(
-      new Response("synthesized response body", { status: 308 })
-    ));
-  }
-
   else if (ev.request.url.includes("synthesized-headers.txt")) {
     ev.respondWith(Promise.resolve(
       new Response("synthesized response body", {
         headers: {
           "X-Custom-Greeting": "Hello"
         }
       })
     ));

--- a/netwerk/protocol/http/nsHttpChannel.cpp
+++ b/netwerk/protocol/http/nsHttpChannel.cpp
@@ -2946,21 +2946,18 @@ nsHttpChannel::OnCacheEntryCheck(nsICach
     rv = mCachedResponseHead->Parse((char *) buf.get());
     NS_ENSURE_SUCCESS(rv, rv);
     buf.Adopt(0);
 
     bool isCachedRedirect = WillRedirect(mCachedResponseHead);
 
     // Do not return 304 responses from the cache, and also do not return
     // any other non-redirect 3xx responses from the cache (see bug 759043).
-    // However, if this is a synthesized cache entry we don't care what the
-    // content is and will return it regardless.
     NS_ENSURE_TRUE((mCachedResponseHead->Status() / 100 != 3) ||
-                   isCachedRedirect ||
-                   mInterceptCache == INTERCEPTED, NS_ERROR_ABORT);
+                   isCachedRedirect, NS_ERROR_ABORT);
 
     // Don't bother to validate items that are read-only,
     // unless they are read-only because of INHIBIT_CACHING or because
     // we're updating the offline cache.
     // Don't bother to validate if this is a fallback entry.
     if (!mApplicationCacheForWrite &&
         (appCache ||
          (mCacheEntryIsReadOnly && !(mLoadFlags & nsIRequest::INHIBIT_CACHING)) ||