Identification of interface elements in Developer Toolbox

Hello Everyone.
I have a problem with Developer toolbox. I’m using the Inspector option to select and identify elements of interface of Thunderbird. All works fine if I select elements of the main window of Thunderbird, as in the picture below:


But when I try to select the elements of other windows, for example, a Write new message window, the Inspector continues to identify main window items:

My question is:
How can I identify other windows (other than the main window) by the Inspector in Developer toolbox?