diff --git a/dotnet/src/webdriver/Firefox/FirefoxDriverService.cs b/dotnet/src/webdriver/Firefox/FirefoxDriverService.cs
index 43b950bed6889..d023c546a4671 100644
--- a/dotnet/src/webdriver/Firefox/FirefoxDriverService.cs
+++ b/dotnet/src/webdriver/Firefox/FirefoxDriverService.cs
@@ -195,6 +195,8 @@ protected override string CommandLineArguments
                     argsBuilder.Append(" --jsdebugger");
                 }
 
+                argsBuilder.Append(string.Format(CultureInfo.InvariantCulture, " --websocket-port {0}", PortUtilities.FindFreePort()));
+
                 return argsBuilder.ToString().Trim();
             }
         }