Question

I’m stuck now, in a background page, I would like use the .html() jQuery method on the popup.html DOM from background.html.

I found something with

var x = chrome.extension.getViews({type:"popup"});

What I have to do with x?

The popup may be closed.

Answer 1

x will be an array of the windows you asked for, which in this case is the popup so should only be one.
Something like this should get you going….

var x = chrome.extension.getViews({type:"popup"});
if (x.length>0){
  $(x[0].document.body).html('I had chicken for lunch!');
}

http://code.google.com/chrome/extensions/extension.html#method-getViews