Mozilla does not have the ability to access the content of your encrypted file, and only keeps it for the time or number of downloads indicated
Anyone you provide with the unique link (including the encryption key) to your encrypted file will be able to download and access that file.
Wtf? URL that contains the encryption key is stored on the Mozilla servers along with file. Thus, they have full access to the uploaded information. To ensure privacy, key must be transmitted through another communication channel. But even in this case it is difficult to detect a possible key leakage.