Starting a browser with a specific profile 10/10/2012
# Starting the browser with a new default profile
profile = Selenium::WebDriver::Firefox::Profile.new
browser = Watir::Browser.new :firefox, :profile => profile

# Starting the browser with a modified profile
profile = Selenium::WebDriver::Firefox::Profile.new
profile.native_events = false
browser = Watir::Browser.new :firefox, :profile => profile

It is sometimes useful to start the browser with a specific profile. It could be due to wanting to have an addon available while running tests (Firebug) or something else, like disabling native events as shown in the example above.