What are the products of the reaction between fluorine and ammonia?
Fluorine reacts with ammonia to give dinitrogen and hydrogen fluoride as the major product.

The Formation of Dinitrogen Tetrafluoride in the Reaction of Fluorine and Ammonia - J. Am. Chem. Soc. 1959, 81 (23), 6338-6339 - states that dinitrogentetrafluoride accounts for 6% of the yield while the major reaction is:


  $\ce{3F2 + 2NH3 → N2 + 6HF}$


The same article quotes in its first paragraph that the result remained the same irrespective of the concentration of the reactants. (In the case of chlorine it matters which reactant is taken in excess)