How do I run Firefox inspector within an iFrame?

I know Chrome's inspector has a selector to choose which frame to use with the console. Firebug has a similar command, cd(window.frames[number]). Is there anything similar in Firefox Devtools? I suppose frame.window.eval could work, but only if it isn't cross-domain.

I was also wondering if there is a highlighter to inspect results of Web-console commands, for example document.getElementsByClassName(...). but you can at least change style of an element programmatically to 'see' it.