diff --git a/components/style/properties/helpers.mako.rs b/components/style/properties/helpers.mako.rs
index cfb7fbbfa45..5e90fc06394 100644
--- a/components/style/properties/helpers.mako.rs
+++ b/components/style/properties/helpers.mako.rs
@@ -930,12 +930,6 @@
                 use values::specified::length::LengthOrPercentageOrAuto;
                 SpecifiedValue(MozLength::LengthOrPercentageOrAuto(LengthOrPercentageOrAuto::zero()))
             }
-
-            /// Returns a value representing a `0%` length.
-            pub fn zero_percent() -> Self {
-                use values::specified::length::LengthOrPercentageOrAuto;
-                SpecifiedValue(MozLength::LengthOrPercentageOrAuto(LengthOrPercentageOrAuto::zero_percent()))
-            }
         }
         % endif
 
diff --git a/components/style/properties/longhand/position.mako.rs b/components/style/properties/longhand/position.mako.rs
index cfc54d2d00c..795aa7513e4 100644
--- a/components/style/properties/longhand/position.mako.rs
+++ b/components/style/properties/longhand/position.mako.rs
@@ -167,11 +167,18 @@ ${helpers.predefined_type("order", "Integer", "0",
 // and should be converted to just LengthOrPercentage.
 % if product == "gecko":
     // FIXME: Gecko doesn't support content value yet.
-    ${helpers.gecko_size_type("flex-basis", "MozLength", "auto()",
-                              logical=False,
-                              spec="https://drafts.csswg.org/css-flexbox/#flex-basis-property",
-                              extra_prefixes="webkit",
-                              animation_value_type="MozLength")}
+    //
+    // FIXME(emilio): I suspect this property shouldn't allow quirks, and this
+    // was just a mistake.
+    ${helpers.predefined_type(
+        "flex-basis",
+        "MozLength",
+        "computed::MozLength::auto()",
+        extra_prefixes="webkit",
+        animation_value_type="ComputedValue",
+        allow_quirks=True,
+        spec="https://drafts.csswg.org/css-flexbox/#flex-basis-property"
+    )}
 % else:
     // FIXME: This property should be animatable.
     ${helpers.predefined_type("flex-basis",
diff --git a/components/style/values/specified/length.rs b/components/style/values/specified/length.rs
index b1d7a19e2c5..1e669e5b8c8 100644
--- a/components/style/values/specified/length.rs
+++ b/components/style/values/specified/length.rs
@@ -933,6 +933,7 @@ impl LengthOrPercentageOrAuto {
     }
 
     /// Returns a value representing `0%`.
+    #[inline]
     pub fn zero_percent() -> Self {
         LengthOrPercentageOrAuto::Percentage(computed::Percentage::zero())
     }
@@ -1142,6 +1143,18 @@ impl MozLength {
         )?;
         Ok(MozLength::LengthOrPercentageOrAuto(length))
     }
+
+    /// Returns `auto`.
+    #[inline]
+    pub fn auto() -> Self {
+        MozLength::LengthOrPercentageOrAuto(LengthOrPercentageOrAuto::auto())
+    }
+
+    /// Returns `0%`.
+    #[inline]
+    pub fn zero_percent() -> Self {
+        MozLength::LengthOrPercentageOrAuto(LengthOrPercentageOrAuto::zero_percent())
+    }
 }
 
 /// A value suitable for a `max-width` or `max-height` property.