Watir-webdriver 在不同作業系統時會報錯.

想請教各位先進一個在使用Watir-webdriver時會遇到的問題

環境如下: Mac 10.7.5 與Ubuntu 12.04
Ruby 版本 : 1.9.2-p320
安裝Ruby 方式: 皆同樣是採RVM安裝, 且獨立用gemset

安裝的gem :

addressable (2.3.2)
bundler (1.2.1)
childprocess (0.3.5)
ffi (1.1.5)
headless (0.3.1)
libwebsocket (0.1.5)
multi_json (1.3.6)
nokogiri (1.5.5)
rake (0.9.2.2)
rb-readline (0.4.2)
rubygems-bundler (1.1.0)
rubyzip (0.9.9)
rvm (1.11.3.5)
selenium-webdriver (2.25.0)
watir-webdriver (0.6.1)

code 都按照http://watirwebdriver.com/ 所述

require 'watir-webdriver'
b = Watir::Browser.new
b.goto 'bit.ly/watir-webdriver-demo'
b.text_field(:id => 'entry_0').set 'your name'
b.select_list(:id => 'entry_1').select 'Ruby'
b.select_list(:id => 'entry_1').selected? 'Ruby'
b.button(:name => 'submit').click
b.text.include? 'Thank you'

但是在Mac下就可以正常開啟Firefox, 但在Ubuntu 12.04就會報錯

錯誤訊息如下:

/home/user/.rvm/rubies/ruby-1.9.2-p320/lib/ruby/1.9.1/uri/common.rb:126:in split': bad URI(absolute but no path): http:// (URI::InvalidURIError)
from /home/user/.rvm/rubies/ruby-1.9.2-p320/lib/ruby/1.9.1/uri/common.rb:174:inparse'
from /home/user/.rvm/rubies/ruby-1.9.2-p320/lib/ruby/1.9.1/uri/common.rb:628:in parse'
from /home/user/.rvm/gems/ruby-1.9.2-p320@watir/gems/selenium-webdriver-2.25.0/lib/selenium/webdriver/remote/http/default.rb:91:innew_http_client'
from /home/user/.rvm/gems/ruby-1.9.2-p320@watir/gems/selenium-webdriver-2.25.0/lib/selenium/webdriver/remote/http/default.rb:16:in http'
from /home/user/.rvm/gems/ruby-1.9.2-p320@watir/gems/selenium-webdriver-2.25.0/lib/selenium/webdriver/remote/http/default.rb:82:inresponse_for'
from /home/user/.rvm/gems/ruby-1.9.2-p320@watir/gems/selenium-webdriver-2.25.0/lib/selenium/webdriver/remote/http/default.rb:38:in request'
from /home/user/.rvm/gems/ruby-1.9.2-p320@watir/gems/selenium-webdriver-2.25.0/lib/selenium/webdriver/remote/http/common.rb:40:incall'
from /home/user/.rvm/gems/ruby-1.9.2-p320@watir/gems/selenium-webdriver-2.25.0/lib/selenium/webdriver/remote/bridge.rb:598:in raw_execute'
from /home/user/.rvm/gems/ruby-1.9.2-p320@watir/gems/selenium-webdriver-2.25.0/lib/selenium/webdriver/remote/bridge.rb:92:increate_session'
from /home/user/.rvm/gems/ruby-1.9.2-p320@watir/gems/selenium-webdriver-2.25.0/lib/selenium/webdriver/remote/bridge.rb:68:in initialize'
from /home/user/.rvm/gems/ruby-1.9.2-p320@watir/gems/selenium-webdriver-2.25.0/lib/selenium/webdriver/firefox/bridge.rb:32:ininitialize'
from /home/user/.rvm/gems/ruby-1.9.2-p320@watir/gems/selenium-webdriver-2.25.0/lib/selenium/webdriver/common/driver.rb:31:in new'
from /home/user/.rvm/gems/ruby-1.9.2-p320@watir/gems/selenium-webdriver-2.25.0/lib/selenium/webdriver/common/driver.rb:31:infor'
from /home/user/.rvm/gems/ruby-1.9.2-p320@watir/gems/selenium-webdriver-2.25.0/lib/selenium/webdriver.rb:65:in for'
from /home/user/.rvm/gems/ruby-1.9.2-p320@watir/gems/watir-webdriver-0.6.1/lib/watir-webdriver/browser.rb:35:ininitialize'
from test.rb:7:in new'
from test.rb:7:in'

基本上在 b = Watir::Browser.new , 這一行執行時就會產生錯誤,
但同樣的code在Mac就沒有什麼問題, 甚至在WIndows也沒有什麼問題,
所以想請教各位先進是否有什麼解決的方法, 感謝