Add "ftp", "ftps", and "sftp" to the list of protocols available for registration via registerProtocolHandler(). FTP is now deprecated and will imminently be removed from the codebase. Allowing websites to register themselves as handlers for ftp:// URLs makes it possible to build easy to use gateways for legacy ftp sites. In addition we propose adding related protocols "ftps" and "sftp" to the list. Google Chrome/Chromium was not handling these URL schemes.
Same as other schemes in registerProtocolHandler. Since ftp was a protocol that used to be supported by the browser, internal ftp links might exist that assume in-browser support in assessing their security risks. A custom protocol handler will necessarily expose ftp URLs to the handler. Registering one may violate administrator assumptions about the URLs not leaving their organization when users click on them.