After reading the previous discussions listed in this thread it seems you like asking kind of the same question over and over again?

Anyway: I don't know "Watir", never heard of. But if I follow the non-link you gave I read immediately "Powered by Selenium"

That's straightforward. There are some selenium modules on CPAN which should answer this question for good. The API for Selenium should be "equivalent" independently from the client language.

See also Selenium (software) if you don't know what's about.