The amount of apps that allow for addition cloud storage are aplenty on BlackBerry 10. You have MEGA, Dropbox, Box and even OneDrive built in but among those available, MediaFire is missing from the list. MediaFire in case you're not aware, offers you up to 10GB of free cloud storage for all your files so it's a nice spot to upload pictures, music, documents, videos and whatever else you may want.
Fireball is a native app for all BlackBerry 10 devices running 10.2.1 and up that offers up access to MediaFire for uploading all the above in a beautiful UI designed for BlackBerry 10. You simply log into your account and from there you can upload any files you wish, create new folders, share files and more and right now it's on sale for only $.99. Check out the full list of features.
Of course, MediaFire does offer a free Android app but if you're not interested in running the Android version then Fireball is the best alternative for BlackBerry 10. On top of it already being a great app, the developer is looking for more ways to improve the app as well and is open to feedback in the CrackBerry Forums. If you purchase it, and can think of ways to improve it, be sure to let him know.