What does @-moz-document url-prefix() do?

Question

In Simon Collison\'s new old Responsive Web Design, in the CSS, there are several declarations like this:

@-moz-document url-prefix() {
  .f         


        

Answer 1

@supports (-moz-appearance:none) {...} worked for me in cases where @-moz-document url-prefix() {...} didn't.