MediaFire Desktop for Mac creates a folder in your Home directory and automatically syncs everything placed inside with the cloud. It runs continuously in the background and adds an icon on the menu bar and in the Finder Favorites sidebar for quick access. The free tier of the service requires online registration and provides you with 10GB of free storage.
Due to its deep Finder integration, MediaFire Desktop for Mac requests an administrative password during setup. You will also be asked to register with the service to get 10GB of free online storage, if you don't have a MediaFire account already. During setup the app creates a folder in your Home directory and links it to your MediaFire account; anything you place inside it is automatically uploaded to the cloud. A nice feature is the ability to take screenshots, add captions and arrows to them in MediaFire Desktop, and then automatically upload them.
If you want to protect yourself against accidental data loss, you should try MediaFire Desktop for Mac. If, on the other hand, you need a sync solution between various devices and apps, a more popular platform such as Dropbox or Google Drive will better serve your needs.