I have a similar issue, when downloading multiple files quickly (you can just download the same thing again and again, around 10).

It will crash my phone, then fail to boot, and load the recovery screen saying "Can't load Android system. Your data may be corrupt".

Rebooting again loads the OS fine, and if you want to download things the workaround is to put the phone into airplane mode to stop mobile. No idea why this happens but its a little worrying that it messes with the mobile connection at all.

Edit: scratch that, it happens even if airplane mode is on. I wonder if its something feature specific because my phone is dual sim and its almost like it gets unmounted

Hi

This is something that our developers are looking into and hope to have resolved very soon. You can follow progress on this at:

https://bugzilla.mozilla.org/show_bug.cgi?id=1847141