Significantly improved specification conformance for the Window object, including named properties and changing various data properties to accessor properties. This is not likely to be breaking, but since it's a complex change to such a core object, we're happy to do another beta testing release with this included before graduating the v27 line to stable.
Additionally, updated cssstyle to v4.4.0, which brings along various conformance fixes to the CSSStyleDeclaration object and its properties.