--- a/servo/components/style/gecko/pseudo_element_definition.mako.rs
+++ b/servo/components/style/gecko/pseudo_element_definition.mako.rs
@@ -113,17 +113,22 @@ impl PseudoElement {
     /// Returns `None` if the pseudo-element is not recognised.
     #[inline]
     pub fn from_slice(s: &str, in_ua_stylesheet: bool) -> Option<Self> {
         use std::ascii::AsciiExt;
 
         % for pseudo in PSEUDOS:
             if in_ua_stylesheet || PseudoElement::${pseudo.capitalized()}.exposed_in_non_ua_sheets() {
                 if s.eq_ignore_ascii_case("${pseudo.value[1:]}") {
+                // ::moz-placeholder is an alias for ::placeholder
+                % if pseudo.value[1:] == "-moz-placeholder" :
+                    return Some(PseudoElement::Placeholder)
+                % else :
                     return Some(PseudoElement::${pseudo.capitalized()})
+                % endif
                 }
             }
         % endfor
 
         None
     }
 
     /// Returns the pseudo-element's definition as a string, with only one colon