How to "unhide" popup window after calling window.alert()?

[dte...@gmail.com]

Hi,

Using Firefox 47 and 48.
I’ve got a WebExtenstion that calls window.alert().
The problem is when window.alert() is called, the Extension’s window, which is a popup, is hidden and is not “unhidden” when the alert window is closed.
I know the window is being hidden, because if I "Disable autohide" in the debugging settings (https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Debugging#Disable_autohide) the popup window remains visible.
I’ve tried to use the nsIPromptService, like the example in https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XPCOM/Reference/Interface/nsIPromptService
But the Components object does not have a classes member.

Can anyone tell me how to either restore my main window, or how to use the nsIPromptService?

Thanks,