How do I know if this app has down loaded?

I contacted Mozilla because I was finding it difficult to find particular email addresses I wished to use and Mozilla were kind enough to send me an app which should resolve that matter. I went through the motions of downloading the app but have no idea if it did actually download although I suspect that It didn’t. By the way, I have no idea if this is the correct address for my question and if not I apologise.

Regards,

Brian M. Leahy