anchor.diff:          infoLog: isCirrus ? stdout : DevNull(),
         );
   
  +      // Using a profile on opening will prevent popups related to profiles.
  +      final _profile = '''
  +user_pref("browser.shell.checkDefaultBrowser", false);
  +user_pref("dom.disable_open_during_load", false);
  +user_pref("dom.max_script_run_time", 0);
  +''';
  +
  +      final Directory temporaryProfileDirectory = Directory(
  +          path.join(environment.webUiDartToolDir.path, 'firefox_profile'));
  +
         // A good source of various Firefox Command Line options:
         // https://developer.mozilla.org/en-US/docs/Mozilla/Command_Line_Options#Browser
         //
  -      var dir = createTempDir();
  +      if (temporaryProfileDirectory.existsSync()) {
  +        temporaryProfileDirectory.deleteSync();
  +      }
  +      temporaryProfileDirectory.createSync(recursive: true);
  +
  +      File(path.join(temporaryProfileDirectory.path, 'prefs.js'))
  +          .writeAsStringSync(_profile);
         bool isMac = Platform.isMacOS;
         var args = [
           url.toString(),
  +        '--profile',
  +        '${temporaryProfileDirectory.path}',
           '--headless',
           '-width $kMaxScreenshotWidth',
           '-height $kMaxScreenshotHeight',
  
positive.code:       ];
  
        final Process process =
            await Process.start(installation.executable, args,
              workingDirectory: dir);
  
        remoteDebuggerCompleter.complete(
            getRemoteDebuggerUrl(Uri.parse('http://localhost:$kDevtoolsPort')));
  
        unawaited(process.exitCode
            .then((_) => Directory(dir).deleteSync(recursive: true)));
  
        return process;
      }, remoteDebuggerCompleter.future);
  
negative.code: 
  import 'package:pedantic/pedantic.dart';
  
  import 'package:path/path.dart' as path;
  import 'package:test_core/src/util/io.dart'; // ignore: implementation_imports
  
  import 'browser.dart';
  import 'common.dart';
  import 'environment.dart';
  import 'firefox_installer.dart';
  
  /// A class for running an instance of Firefox.
  ///
  