How to analyze popup window with Inspector on Firefox?
Solution 1:
The focus issue has an official workaround:
It's hard to debug popups, because the browser hides them as soon as you click outside them. There is a way to disable this behavior. Click the toolbox menu and select Disable popup auto-hide.
Also note that:
This change is not persistent across browser restarts. When you close the browser toolbox, the setting will be cleared.