I was quite surprised to see my own files deleted as well.
After that I came across a FAQ entry on the website
“There is currently no time limit on how long uploaded files will be stored as long as you access your account (i.e. login to your account) at least once every 60 days OR at least one of your files is accessed (i.e. downloaded) every 30 days. If your account is not accessed within the time limit, then the files in your account will be cleared. MediaPro subscribers’ uploaded files will remain forever as long as the account is active.
If you are a Mediafire free user and your files were deleted due to inactivity, they are deleted from all servers and cannot be retrieved.“
This means that files stored on MediaFire will be deleted without any kind of notification if you don’t log in every 2 months. This is something which is quite scary to me.
So be careful when using MediaFire and don’t store any files on there which you haven’t stored anywhere else, or be sure to use your account enough to not get your files deleted.