Enquanto usava o Watir Webdriver v0.9.1 para trilhos (junto com o Selenium Webdriver 2.53.1), o Firefox estava abrindo quando

  browser = Watir::Browser.new :firefox

foi chamado. Agora, no entanto, ele falha nessa linha com

unable to bind to locking port 7054 within 45 seconds
    @ /Users/andmcadams/.rvm/gems/ruby-2.0.0-p648/gems/selenium-webdriver-2.53.1/lib/selenium/webdriver/common/socket_lock.rb:59:in `lock'
      /Users/andmcadams/.rvm/gems/ruby-2.0.0-p648/gems/selenium-webdriver-2.53.1/lib/selenium/webdriver/common/socket_lock.rb:40:in `locked'
      /Users/andmcadams/.rvm/gems/ruby-2.0.0-p648/gems/selenium-webdriver-2.53.1/lib/selenium/webdriver/firefox/launcher.rb:51:in `launch'
      /Users/andmcadams/.rvm/gems/ruby-2.0.0-p648/gems/selenium-webdriver-2.53.1/lib/selenium/webdriver/firefox/bridge.rb:43:in `initialize'
      /Users/andmcadams/.rvm/gems/ruby-2.0.0-p648/gems/selenium-webdriver-2.53.1/lib/selenium/webdriver/common/driver.rb:53:in `new'
      /Users/andmcadams/.rvm/gems/ruby-2.0.0-p648/gems/selenium-webdriver-2.53.1/lib/selenium/webdriver/common/driver.rb:53:in `for'
      /Users/andmcadams/.rvm/gems/ruby-2.0.0-p648/gems/selenium-webdriver-2.53.1/lib/selenium/webdriver.rb:84:in `for'
      /Users/andmcadams/.rvm/gems/ruby-2.0.0-p648/gems/watir-webdriver-0.9.1/lib/watir-webdriver/browser.rb:46:in `initialize'
      test/integration/like_fanpage_task_test.rb:40:in `new'
      test/integration/like_fanpage_task_test.rb:40:in `block (2 levels) in <class:LikeFanpageTaskTest>'

Pareceu fazê-lo aleatoriamente, pois não alterei o código de sua forma de trabalho e essa linha é a primeira linha chamada. Eu tenho o Firefox 37.0.2, que funcionou anteriormente. Tentei reiniciar o computador, eliminando processos relacionados ao ruby e Firefox e iniciando-os novamente e reinstalando o Firefox, mas sem sucesso.