--- a/servo/components/style/properties/gecko.mako.rs
+++ b/servo/components/style/properties/gecko.mako.rs
@@ -607,22 +607,16 @@ impl Debug for ${style_struct.gecko_stru
     # Make a list of types we can't auto-generate.
     #
     force_stub = [];
     # These live in an nsFont member in Gecko. Should be straightforward to do manually.
     force_stub += ["font-variant"]
     # These have unusual representations in gecko.
     force_stub += ["list-style-type"]
 
-    # These are part of shorthands so we must include them in stylo builds,
-    # but we haven't implemented the stylo glue for the longhand
-    # so we generate a stub
-    force_stub += ["flex-basis", # position
-                   ]
-
     # Types used with predefined_type()-defined properties that we can auto-generate.
     predefined_types = {
         "length::LengthOrAuto": impl_style_coord,
         "length::LengthOrNormal": impl_style_coord,
         "Length": impl_absolute_length,
         "Position": impl_position,
         "LengthOrPercentage": impl_style_coord,
         "LengthOrPercentageOrAuto": impl_style_coord,

--- a/servo/components/style/properties/longhand/position.mako.rs
+++ b/servo/components/style/properties/longhand/position.mako.rs
@@ -190,23 +190,26 @@
         0
     }
 
     fn parse(_context: &ParserContext, input: &mut Parser) -> Result<SpecifiedValue, ()> {
         specified::parse_integer(input)
     }
 </%helpers:longhand>
 
+// FIXME: Gecko doesn't support content value yet.
 // FIXME: This property should be animatable.
 ${helpers.predefined_type("flex-basis",
+                          "LengthOrPercentageOrAuto" if product == "gecko" else
                           "LengthOrPercentageOrAutoOrContent",
+                          "computed::LengthOrPercentageOrAuto::Auto" if product == "gecko" else
                           "computed::LengthOrPercentageOrAutoOrContent::Auto",
                           spec="https://drafts.csswg.org/css-flexbox/#flex-basis-property",
                           extra_prefixes="webkit",
-                          animatable=False)}
+                          animatable=True if product == "gecko" else False)}
 
 % for (size, logical) in ALL_SIZES:
     <%
       spec = "https://drafts.csswg.org/css-box/#propdef-%s"
       if logical:
         spec = "https://drafts.csswg.org/css-logical-props/#propdef-%s"
     %>
     // width, height, block-size, inline-size

--- a/servo/components/style/properties/shorthand/position.mako.rs
+++ b/servo/components/style/properties/shorthand/position.mako.rs
@@ -44,17 +44,22 @@
             self.flex_wrap.to_css(dest)
         }
     }
 </%helpers:shorthand>
 
 <%helpers:shorthand name="flex" sub_properties="flex-grow flex-shrink flex-basis" extra_prefixes="webkit"
                     spec="https://drafts.csswg.org/css-flexbox/#flex-property">
     use parser::Parse;
-    use values::specified::{Number, NoCalcLength, LengthOrPercentageOrAutoOrContent};
+    use values::specified::{Number, NoCalcLength};
+    % if product == "gecko":
+        use values::specified::LengthOrPercentageOrAuto;
+    % else:
+        use values::specified::LengthOrPercentageOrAutoOrContent;
+    % endif
 
     pub fn parse_flexibility(input: &mut Parser)
                              -> Result<(Number, Option<Number>),()> {
         let grow = try!(Number::parse_non_negative(input));
         let shrink = input.try(Number::parse_non_negative).ok();
         Ok((grow, shrink))
     }
 
@@ -62,43 +67,56 @@
         let mut grow = None;
         let mut shrink = None;
         let mut basis = None;
 
         if input.try(|input| input.expect_ident_matching("none")).is_ok() {
             return Ok(Longhands {
                 flex_grow: Number(0.0),
                 flex_shrink: Number(0.0),
-                flex_basis: LengthOrPercentageOrAutoOrContent::Auto
+                % if product == "gecko":
+                    flex_basis: LengthOrPercentageOrAuto::Auto
+                % else:
+                    flex_basis: LengthOrPercentageOrAutoOrContent::Auto
+                % endif
+
             })
         }
         loop {
             if grow.is_none() {
                 if let Ok((flex_grow, flex_shrink)) = input.try(parse_flexibility) {
                     grow = Some(flex_grow);
                     shrink = flex_shrink;
                     continue
                 }
             }
             if basis.is_none() {
-                if let Ok(value) = input.try(|i| LengthOrPercentageOrAutoOrContent::parse(context, i)) {
+                % if product == "gecko":
+                    if let Ok(value) = input.try(|i| LengthOrPercentageOrAuto::parse(context, i)) {
+                % else:
+                    if let Ok(value) = input.try(|i| LengthOrPercentageOrAutoOrContent::parse(context, i)) {
+                % endif
                     basis = Some(value);
                     continue
                 }
             }
             break
         }
 
         if grow.is_none() && basis.is_none() {
             return Err(())
         }
         Ok(Longhands {
             flex_grow: grow.unwrap_or(Number(1.0)),
             flex_shrink: shrink.unwrap_or(Number(1.0)),
-            flex_basis: basis.unwrap_or(LengthOrPercentageOrAutoOrContent::Length(NoCalcLength::zero()))
+            % if product == "gecko":
+                flex_basis: basis.unwrap_or(LengthOrPercentageOrAuto::Length(NoCalcLength::zero()))
+            % else:
+                flex_basis: basis.unwrap_or(LengthOrPercentageOrAutoOrContent::Length(NoCalcLength::zero()))
+            % endif
         })
     }
 
     impl<'a> ToCss for LonghandsToSerialize<'a>  {
         fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
             try!(self.flex_grow.to_css(dest));
             try!(write!(dest, " "));