font-FiraCode/features/onum.fea

sub zero by zero.tosf;
sub zero.zero by zero.zero.tosf;
sub one by one.tosf;
sub two by two.tosf;
sub three by three.tosf;
sub four by four.tosf;
sub five by five.tosf;
sub six by six.tosf;
sub seven by seven.tosf;
sub eight by eight.tosf;
sub nine by nine.tosf;
sub x.multiply by x.multiply.tosf;