Thank you again!
When I send message from context of iframe there issender.frameId property which is actually ‘windowId’ which is needed for me in background script to print particular frame.
For example if I want to print desired frame I simple send message from frame to background script.
In practice I tested that sender.frameId is windowsId that I can give as parameter of activeTab.linkedBrowser.print(windowID, printSettings, null);
I can’t find any proof at documentation that frameId is windowId.