--- a/dom/workers/WorkerPrivate.cpp
+++ b/dom/workers/WorkerPrivate.cpp
@@ -2032,16 +2032,22 @@ public:
     // Assumes that WorkerJSRuntimeStats will hold a reference to |path|, and
     // not a copy, as TryToMapAddon() may later modify if.
     nsCString path;
     WorkerJSRuntimeStats rtStats(path);
 
     {
       MutexAutoLock lock(mMutex);
 
+      if (!mWorkerPrivate ||
+          !mWorkerPrivate->BlockAndCollectRuntimeStats(&rtStats, aAnonymize)) {
+        // Returning NS_OK here will effectively report 0 memory.
+        return NS_OK;
+      }
+
       path.AppendLiteral("explicit/workers/workers(");
       if (aAnonymize && !mWorkerPrivate->Domain().IsEmpty()) {
         path.AppendLiteral("<anonymized-domain>)/worker(<anonymized-url>");
       } else {
         nsCString escapedDomain(mWorkerPrivate->Domain());
         if (escapedDomain.IsEmpty()) {
           escapedDomain += "chrome";
         } else {
@@ -2051,22 +2057,16 @@ public:
         path.AppendLiteral(")/worker(");
         NS_ConvertUTF16toUTF8 escapedURL(mWorkerPrivate->ScriptURL());
         escapedURL.ReplaceChar('/', '\\');
         path.Append(escapedURL);
       }
       path.AppendPrintf(", 0x%p)/", static_cast<void*>(mWorkerPrivate));
 
       TryToMapAddon(path);
-
-      if (!mWorkerPrivate ||
-          !mWorkerPrivate->BlockAndCollectRuntimeStats(&rtStats, aAnonymize)) {
-        // Returning NS_OK here will effectively report 0 memory.
-        return NS_OK;
-      }
     }
 
     return xpc::ReportJSRuntimeExplicitTreeStats(rtStats, path,
                                                  aCallback, aClosure,
                                                  aAnonymize);
   }
 
 private: