Is there a way to change context to iframe in javascript console?

Chrome 15 allows you to change the scope of the console. On the bottom of the console, next to the clear console button, there is a menu that says <top frame> which will give a list of available frames:

Firefox has a similar feature currently in development:

You can also navigate across frames using the command line:

var frame = document.getElementById("frame1").contentWindow;
cd(frame);