Use webdriver to build fonctionnal tests
Selenium has lots of limits (can't upload a file for example)
Webdriver is on os, so no limits.
Cons: Webdriver has no python binding to IE atm, but i m sure it can be done.
Work on this began at the post-conference sprints in 2010. plone.app.testing (included in 4.1) has a webdriver layer. Other packages have already begun building tests against this.
Dylan Jay commented
zc.testbrowser.real uses firefox to provide js support for the existing testbrowser/doctest tests. It uses the same API has zc.testbrowser. It would be fantastic to have another testbrowser API compatible backend using webdriver or selenium RC. testbrowser is an awesome api for right functional tests as its easy to fit in your head making it great for test driven development so I wouldn't agree with any change to that API.