Mozilla developed a sharing platform used via browser.
Your data gets encrypted and will delete itself after 24h or if someone downloads it.
For the encryption Mozilla uses "Web Cryptography JavaScript API" with the AES-GCM algorythm.
The link you sent a person will contain the key for the download but won´t be sent to mozilla.
The idea behind the project is to share content in a fast and easy way, without being
limited to the small file sizes E-Mails can handle or with downsides like compression on Facebook.