Hi

Please can you check for updates to Firefox for Android in the Google Play store app on your device. We have just released an update that should fix this issue.

Thank you for your answer, but the update did not solve my issue... still not able to download any files !

Well finally after some tries it seems to work fine... thats funny because I had this problem for weeks and weeks, but as soon as I complain Mozilla published a patch which correct my issue. Chance do funny things sometimes.