In the console of the Developer Tools in Chrome, the 'focus' can be changed to an IFRAME using the dropdown selector, shown here:
How can that be done in Internet Explorer 11, in the F12 Developer Tools?
(I know that the contents of IFRAMEs can also be accessed using frames[0]...
.)
In IE from versions 9 onwards you can use the cd() command in the console to change the frame targeting you need to pass in a reference to the frame.