Comparison Chart

IE/Safari/Firefox/Chrome SupportYesYesDiffering libraries
Test RecorderYes, on all platformsFirefox Plugin onlyYes
Cross DomainYesFirefox and IE only in trusted mode.Yes
Supported LanguagesPython, JavaScript, RubyManyRuby
Integrated Debugging ToolsFirebug and Firebug Lite, InspectorNoneNone
Proxy ManipulationYes, could be betterNoN/A, Watir doesn’t use a proxy

Integrated Development Environment

Full Featured Recorder: One click and the IDE writes your test for you
DOM Explorer: Explore the DOM, aids in test editing and debugging
Assertion Explorer: Quickly generate action validating the state of your application
Test Saving and Playback
Real Time Performance and Output Information

Firebug Lite integration for debugging in all supported browsers

Interactive Python Server

Convenience functionality for launching browsers
PDB debugging support
Test loading and running
DOM query functionality
Reporting helpers