diff --git a/components/style/properties/longhand/box.mako.rs b/components/style/properties/longhand/box.mako.rs
index f80a42c88d2..f45973063b5 100644
--- a/components/style/properties/longhand/box.mako.rs
+++ b/components/style/properties/longhand/box.mako.rs
@@ -19,6 +19,8 @@
             list-item flex
             none
         """.split()
+        if product == "gecko":
+            values += "-moz-box -moz-inline-box".split()
         experimental_values = set("flex".split())
     %>
     pub use self::computed_value::T as SpecifiedValue;
diff --git a/ports/geckolib/properties.mako.rs b/ports/geckolib/properties.mako.rs
index 387f5e02edb..4f92ecc5b37 100644
--- a/ports/geckolib/properties.mako.rs
+++ b/ports/geckolib/properties.mako.rs
@@ -632,7 +632,8 @@ fn static_assert() {
     // infrastructure for preffing certain values.
     <% display_keyword = Keyword("display", "inline block inline-block table inline-table table-row-group " +
                                             "table-header-group table-footer-group table-row table-column-group " +
-                                            "table-column table-cell table-caption list-item flex none") %>
+                                            "table-column table-cell table-caption list-item flex none " +
+                                            "-moz-box -moz-inline-box") %>
     <%call expr="impl_keyword('display', 'mDisplay', display_keyword, True)"></%call>
 
     // overflow-y is implemented as a newtype of overflow-x, so we need special handling.