--- a/toolkit/xre/nsAppRunner.cpp
+++ b/toolkit/xre/nsAppRunner.cpp
@@ -3808,16 +3808,19 @@ XREMain::XRE_mainStartup(bool* aExitFlag
     }
   }
 
   if (!newInstance) {
     nsAutoCString program(gAppData->remotingName);
     ToLowerCase(program);
 
     const char* username = getenv("LOGNAME");
+    if (!username) {
+      username = "";
+    }
     const char* profile  = nullptr;
 
     RemoteResult rr = ParseRemoteCommandLine(program, &profile, &username);
     if (rr == REMOTE_ARG_BAD) {
       return 1;
     }
 
     nsCOMPtr<nsIFile> mutexDir;