What is "f-fcsr"

In cryptography, F-FCSR is a stream cipher developed by Thierry Berger, François Arnault, and Cédric Lauradoux. The core of the cipher is a Feedback with Carry Shift Register (FCSR) automaton, which is similar to a LFSR, but they perform operations with carries so their transition function is nonlinear.

F-FCSR one of the eight algorithms selected for the eCRYPT networks eSTREAM Portfolio, but was later removed because after analysis showed weaknesses.