Unlike most other file sharing services, Firefox Send doesn't encrypt users' data after it arrives on the company's servers (thus allowing the company itself or anyone with access to that company's servers to see what's in the files), but before, on the user's local machine. At the time, users were limited to sending files up to 1 GB and the created link to the file would "expire" after 1 download or 24 hours (whichever comes first). You can send files up to 2.5GB using this service.
We first met Firefox Send a year ago as one of the company's "Test Pilot" experiments. You can also limit the number of times they're downloaded.
Given that the files are encrypted and aren't stored, however, it's going to be ruddy hard for anyone to find out what you've sent anyway.
To protect the file with a password for an extra layer of security.More news: Son's heartbreaking post about dad's new donut shop goes viral
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The service is billed as a simple - and free - way to send large files. And it also uses the Web crypto programming interface, which is one of the better-tested ways Internet applications can perform cryptographic operations without having access to decryption keys.
Now, you're probably asking, "why can't I just send my files through email or a cloud storage service like Google Drive?". "Since nothing lingers in the cloud, your personal information stays private", Mozilla said in an Firefox Send explanatory video.