A friend-to-friend with third party storage (or F3F for short) computer network is a particular type of F2F in which people store the files they want to exchange in a third party storage (e.g. FTP, Web, email server).
F3F allow you to upload a file only once, and then all your friends can get it faster from the third party server.
With a third party that adds a standard layer of encryption (e.g. SSL for Gmail or YahooMail) you can prevent your ISP from knowing that you use a F3F and what are the IP addresses of your friends. You should probably choose a third party located in a different country than yours, where logging of IPs is confidential and is trashed after a short period of time.
Essentially, the F3F was a redesign of its earlier F2F sibling, incorporating a slightly more powerful version of the Pratt & Whitney R-1535 than that fitted to the F2F.
Not all F3F fighters went to the Navy.
This aircraft is that of the Squadron Commander, as indicated by the number in the 5-F-1 indentifying code.