One of the issues that affects many of the layout tests on the SquirrelFish branch (as well as much real browsing) is the fact that split window support is not merged quite right. This results in crashes that look like this (observed, for instance, on media/video-controls.html and also on GMail):
ASSERTION FAILED: !thisObj->inherits(&JSDOMWindow::s_info)
(/Volumes/Data/mjs/Work/src/Safari/OpenSource/WebCore/bindings/js/JSDOMWindowBase.cpp:1131 KJS::JSValue* WebCore::windowProtoFuncSetTimeout(KJS::ExecState*, KJS::JSObject*, const KJS::List&))
As far as I can tell, this mostly works now though some details may be wrong.
Is there a specific change that fixed this bug?