I understand that Firefox for Android is opening at times that it is not expected to. In order to better investigate this issue, can you please provide a little more information:

• Do you have it set for any Default apps?
• What is poping open, and what are the steps you are taking right before it opens?

ES File Manager is my default player for almost all media. Firefox is not set to default.

Here is a step by step.

I see a picture I like so I download it. Firefox has now sent me a notification that the download is complete. After eventually closing the browser, I then clear notifications. Upon doing so, Firefox opens, regardless of whether it was running in the background or truly closed.

Thanks