Use --headless=old to stop chrome from displaying things like the first run popup

Runtime/ChromeDevtools/Browser.cs

@@ -72,6 +72,7 @@ namespace bessw.Unity.WebView.ChromeDevTools
                     $"--user-data-dir={Path.Join(Application.temporaryCachePath, "BrowserView")}",
                     $"--remote-debugging-port={debugPort}",
                     $"--remote-allow-origins=http://localhost:{debugPort}",
+                    // might not be needed with headless=old
                     "--hide-crash-restore-bubble",
                     "--disable-first-run-ui",
                     "--no-first-run",
@@ -90,7 +91,9 @@ namespace bessw.Unity.WebView.ChromeDevTools
                 // set headlessBrowser to false to see the browser window
                 if (headless)
                 {
-                    browserProcess.StartInfo.Arguments = string.Concat(browserProcess.StartInfo.Arguments, " --headless=new");
+                    // --headless=old should be sufficient for rendering web pages,
+                    // --headless=new has the drawback that it still opens the first run popup, the crash restore bubble, etc.
+                    browserProcess.StartInfo.Arguments = string.Concat(browserProcess.StartInfo.Arguments, " --headless=old");
                 }
                 else
                 {