--- a/browser/base/content/test/performance/browser_startup_mainthreadio.js
+++ b/browser/base/content/test/performance/browser_startup_mainthreadio.js
@@ -550,16 +550,23 @@ const startupPhases = {
     {
       path: "XREAppFeat:webcompat-reporter@mozilla.org.xpi",
       condition: !WIN,
       ignoreIfUnused: true,
       stat: 1,
       close: 1,
     },
     {
+      // bug 1003968
+      path: "XREAppDist:searchplugins",
+      condition: WIN,
+      ignoreIfUnused: true, // with WebRender enabled this may happen during "before becoming idle"
+      stat: 1,
+    },
+    {
       path: "XCurProcD:extensions",
       condition: WIN,
       stat: 1,
     },
   ],
 
   // Things that are expected to be completely out of the startup path
   // and loaded lazily when used for the first time by the user should
@@ -653,16 +660,23 @@ const startupPhases = {
       stat: 2,
     },
     {
       path: "ProfD:",
       condition: WIN,
       ignoreIfUnused: true,
       stat: 3,
     },
+    {
+      // bug 1003968
+      path: "XREAppDist:searchplugins",
+      condition: WIN,
+      ignoreIfUnused: true, // with WebRender enabled this may happen during "before handling user events"
+      stat: 1,
+    },
   ],
 };
 
 for (let name of [
   "d3d11layers",
   "d3d9video",
   "glcontext",
   "d3d11video",

--- a/browser/components/dirprovider/DirectoryProvider.cpp
+++ b/browser/components/dirprovider/DirectoryProvider.cpp
@@ -59,21 +59,26 @@ DirectoryProvider::GetFile(const char* a
 static void AppendDistroSearchDirs(nsIProperties* aDirSvc,
                                    nsCOMArray<nsIFile>& array) {
   nsCOMPtr<nsIFile> searchPlugins;
   nsresult rv = aDirSvc->Get(XRE_APP_DISTRIBUTION_DIR, NS_GET_IID(nsIFile),
                              getter_AddRefs(searchPlugins));
   if (NS_FAILED(rv)) return;
   searchPlugins->AppendNative(NS_LITERAL_CSTRING("searchplugins"));
 
+  bool exists;
+  rv = searchPlugins->Exists(&exists);
+  if (NS_FAILED(rv) || !exists) return;
+
   nsCOMPtr<nsIFile> commonPlugins;
   rv = searchPlugins->Clone(getter_AddRefs(commonPlugins));
   if (NS_SUCCEEDED(rv)) {
     commonPlugins->AppendNative(NS_LITERAL_CSTRING("common"));
-    array.AppendObject(commonPlugins);
+    rv = commonPlugins->Exists(&exists);
+    if (NS_SUCCEEDED(rv) && exists) array.AppendObject(commonPlugins);
   }
 
   nsCOMPtr<nsIPrefBranch> prefs(do_GetService(NS_PREFSERVICE_CONTRACTID));
   if (prefs) {
     nsCOMPtr<nsIFile> localePlugins;
     rv = searchPlugins->Clone(getter_AddRefs(localePlugins));
     if (NS_FAILED(rv)) return;
 
@@ -82,31 +87,37 @@ static void AppendDistroSearchDirs(nsIPr
     nsAutoCString defLocale;
     rv = prefs->GetCharPref("distribution.searchplugins.defaultLocale",
                             defLocale);
     if (NS_SUCCEEDED(rv)) {
       nsCOMPtr<nsIFile> defLocalePlugins;
       rv = localePlugins->Clone(getter_AddRefs(defLocalePlugins));
       if (NS_SUCCEEDED(rv)) {
         defLocalePlugins->AppendNative(defLocale);
-        array.AppendObject(defLocalePlugins);
-        return;  // all done
+        rv = defLocalePlugins->Exists(&exists);
+        if (NS_SUCCEEDED(rv) && exists) {
+          array.AppendObject(defLocalePlugins);
+          return;  // all done
+        }
       }
     }
 
     // we didn't have a defaultLocale, use the user agent locale
     nsAutoCString locale;
     LocaleService::GetInstance()->GetAppLocaleAsLangTag(locale);
 
     nsCOMPtr<nsIFile> curLocalePlugins;
     rv = localePlugins->Clone(getter_AddRefs(curLocalePlugins));
     if (NS_SUCCEEDED(rv)) {
       curLocalePlugins->AppendNative(locale);
-      array.AppendObject(curLocalePlugins);
-      return;  // all done
+      rv = curLocalePlugins->Exists(&exists);
+      if (NS_SUCCEEDED(rv) && exists) {
+        array.AppendObject(curLocalePlugins);
+        return;  // all done
+      }
     }
   }
 }
 
 NS_IMETHODIMP
 DirectoryProvider::GetFiles(const char* aKey, nsISimpleEnumerator** aResult) {
   if (!strcmp(aKey, NS_APP_DISTRIBUTION_SEARCH_DIR_LIST)) {
     nsCOMPtr<nsIProperties> dirSvc(
@@ -150,16 +161,20 @@ DirectoryProvider::AppendingEnumerator::
     if (!mNext) continue;
 
     char const* const* i = mAppendList;
     while (*i) {
       mNext->AppendNative(nsDependentCString(*i));
       ++i;
     }
 
+    bool exists;
+    rv = mNext->Exists(&exists);
+    if (NS_SUCCEEDED(rv) && exists) break;
+
     mNext = nullptr;
   }
 
   return NS_OK;
 }
 
 DirectoryProvider::AppendingEnumerator::AppendingEnumerator(
     nsISimpleEnumerator* aBase, char const* const* aAppendList)

--- a/toolkit/components/search/SearchService.jsm
+++ b/toolkit/components/search/SearchService.jsm
@@ -1057,20 +1057,16 @@ SearchService.prototype = {
         winPattern: "*.xml",
       });
       try {
         // Add dir to distDirs if it contains any files.
         let { done } = await iterator.next();
         if (!done) {
           distDirs.push(dir);
         }
-      } catch (ex) {
-        if (!(ex instanceof OS.File.Error) || !ex.becauseNoSuchFile) {
-          throw ex;
-        }
       } finally {
         iterator.close();
       }
     }
 
     function notInCacheVisibleEngines(engineName) {
       return !cache.visibleDefaultEngines.includes(engineName);
     }