Suppress "yourdomain.com could not be found" dialog in GeckFX45

Question

I am using GeckFX45 from NuGet to host a webpage for my OAuth2 login, During testing its behavior without internet connection I noticed that I get a dialog generated by the browser saying the URL could not be found. How can I suppress this to I can catch and handle the scenario in my app without alerting user?

My browser code is pretty standard, but for arguments sake included here anyway (Note I am using WPF not Win Forms hence the host control):

    public OAuthLogin2(OAuthActions action, string args = null)
    {
        this.action = action;

        Gecko.Xpcom.Initialize("Firefox");
        host = new WindowsFormsHost();
        browser = new GeckoWebBrowser();
        browser.DocumentCompleted += Browser_DocumentCompleted;
        browser.Navigating += Browser_Navigating;

        browser.NavigationError += Browser_NavigationError;
        browser.NSSError += Browser_NSSError;

        InitializeComponent();

        host.Child = browser;
        GridWeb.Children.Add(host);
    }

Answer 1

I can add a PromptService, but this may not work depending on language;

    public class NoPromptService : PromptService
    {
        public override void Alert(string dialogTitle, string text)
        {
            log.Warn(dialogTitle, new Exception(text));
            if (text.EndsWith("could not be found. Please check the name and try again."))
            {
                // Do Whatever
            }
        }
    }

Add this in constructor:

PromptFactory.PromptServiceCreator = () => new NoPromptService();