A project of a famous company X, codenamed Y, needed an alternative to give to their own employees once Y rolled out to the general public.
Turns out they bought the rights from the organization Z shown in the pic.
X, Y, Z?
American Farm Bureau (Z) recently sold the rights to http://www.fb.com to Facebook (X) [ who else ].
Since facebook launched their messaging service, codenamed Project Titan(Y), every user would get a @facebook.com email id.
So the employees of facebook were made to switch to @fb.com for their internal email ids.