--- a/netwerk/base/nsProtocolProxyService.cpp
+++ b/netwerk/base/nsProtocolProxyService.cpp
@@ -1161,18 +1161,20 @@ nsProtocolProxyService::SetupPACThread(n
         NS_SUCCEEDED(mSystemProxySettings->GetMainThreadOnly(&mainThreadOnly)) &&
         !mainThreadOnly) {
         rv = mPACMan->Init(mSystemProxySettings);
     }
     else {
         rv = mPACMan->Init(nullptr);
     }
 
-    if (NS_FAILED(rv))
+    if (NS_FAILED(rv)) {
+        mPACMan->Shutdown();
         mPACMan = nullptr;
+    }
     return rv;
 }
 
 nsresult
 nsProtocolProxyService::ResetPACThread()
 {
     if (!mPACMan)
         return NS_OK;