Hi This does not sound like a Firefox for Android query, but I will do my best to help. In the Settings menu, under Storage, check to see if the SD card is "mounted" as a storage option. If not, there should be the option to "mount" it as an storage device. Alternatively, you may find that some apps cannot be moved to external storage. Firefox for Android can, but there are some apps that cannot be moved and have to stay (if you wish to keep them) on the device storage. I hope that this helps, but if not, please come back here and we can look into a different solution for you.