diff --git a/components/style/properties/gecko.mako.rs b/components/style/properties/gecko.mako.rs
index d4dfa3bc853..074e4e08579 100644
--- a/components/style/properties/gecko.mako.rs
+++ b/components/style/properties/gecko.mako.rs
@@ -661,9 +661,10 @@ fn static_assert() {
         use gecko_bindings::structs::nsStyleUnit;
         // z-index is never a calc(). If it were, we'd be leaking here, so
         // assert that it isn't.
-        debug_assert!(self.gecko.mZIndex.mUnit != nsStyleUnit::eStyleUnit_Calc);
-        self.gecko.mZIndex.mUnit = other.gecko.mZIndex.mUnit;
-        self.gecko.mZIndex.mValue = other.gecko.mZIndex.mValue;
+        debug_assert!(self.gecko.mZIndex.unit() != nsStyleUnit::eStyleUnit_Calc);
+        unsafe {
+            self.gecko.mZIndex.copy_from_unchecked(&other.gecko.mZIndex);
+        }
     }
 
     pub fn clone_z_index(&self) -> longhands::z_index::computed_value::T {
diff --git a/ports/geckolib/gecko_bindings/structs_debug.rs b/ports/geckolib/gecko_bindings/structs_debug.rs
index 1ad3478eac0..1ac5b06026e 100644
--- a/ports/geckolib/gecko_bindings/structs_debug.rs
+++ b/ports/geckolib/gecko_bindings/structs_debug.rs
@@ -5150,11 +5150,24 @@ pub type nsStyleUnion = nsStyleCoord_h_unnamed_18;
  * the unit is a must before asking for the value in any particular
  * form.
  */
+ /** <div rustbindgen private accessor="unsafe"></div> */
 #[repr(C)]
 #[derive(Debug)]
 pub struct nsStyleCoord {
-    pub mUnit: nsStyleUnit,
-    pub mValue: nsStyleUnion,
+    mUnit: nsStyleUnit,
+    mValue: nsStyleUnion,
+}
+impl nsStyleCoord {
+    #[inline]
+    pub unsafe fn get_mUnit(&self) -> &nsStyleUnit { &self.mUnit }
+    pub unsafe fn get_mUnit_mut(&mut self) -> &mut nsStyleUnit {
+        &mut self.mUnit
+    }
+    #[inline]
+    pub unsafe fn get_mValue(&self) -> &nsStyleUnion { &self.mValue }
+    pub unsafe fn get_mValue_mut(&mut self) -> &mut nsStyleUnion {
+        &mut self.mValue
+    }
 }
 #[repr(C)]
 #[derive(Debug, Copy)]
@@ -5195,11 +5208,26 @@ fn bindgen_test_layout_nsStyleCoord() {
  * This is commonly used to hold the widths of the borders, margins,
  * or paddings of a box.
  */
+ /** <div rustbindgen private accessor="unsafe"></div> */
 #[repr(C)]
 #[derive(Debug)]
 pub struct nsStyleSides {
-    pub mUnits: [nsStyleUnit; 4usize],
-    pub mValues: [nsStyleUnion; 4usize],
+    mUnits: [nsStyleUnit; 4usize],
+    mValues: [nsStyleUnion; 4usize],
+}
+impl nsStyleSides {
+    #[inline]
+    pub unsafe fn get_mUnits(&self) -> &[nsStyleUnit; 4usize] { &self.mUnits }
+    pub unsafe fn get_mUnits_mut(&mut self) -> &mut [nsStyleUnit; 4usize] {
+        &mut self.mUnits
+    }
+    #[inline]
+    pub unsafe fn get_mValues(&self) -> &[nsStyleUnion; 4usize] {
+        &self.mValues
+    }
+    pub unsafe fn get_mValues_mut(&mut self) -> &mut [nsStyleUnion; 4usize] {
+        &mut self.mValues
+    }
 }
 #[test]
 fn bindgen_test_layout_nsStyleSides() {
@@ -5211,11 +5239,26 @@ fn bindgen_test_layout_nsStyleSides() {
  * nsStyleCoord pairs.  This is used to hold the dimensions of the
  * corners of a box (for, e.g., border-radius and outline-radius).
  */
+ /** <div rustbindgen private accessor="unsafe"></div> */
 #[repr(C)]
 #[derive(Debug)]
 pub struct nsStyleCorners {
-    pub mUnits: [nsStyleUnit; 8usize],
-    pub mValues: [nsStyleUnion; 8usize],
+    mUnits: [nsStyleUnit; 8usize],
+    mValues: [nsStyleUnion; 8usize],
+}
+impl nsStyleCorners {
+    #[inline]
+    pub unsafe fn get_mUnits(&self) -> &[nsStyleUnit; 8usize] { &self.mUnits }
+    pub unsafe fn get_mUnits_mut(&mut self) -> &mut [nsStyleUnit; 8usize] {
+        &mut self.mUnits
+    }
+    #[inline]
+    pub unsafe fn get_mValues(&self) -> &[nsStyleUnion; 8usize] {
+        &self.mValues
+    }
+    pub unsafe fn get_mValues_mut(&mut self) -> &mut [nsStyleUnion; 8usize] {
+        &mut self.mValues
+    }
 }
 #[test]
 fn bindgen_test_layout_nsStyleCorners() {
diff --git a/ports/geckolib/gecko_bindings/structs_release.rs b/ports/geckolib/gecko_bindings/structs_release.rs
index 8ce95c33632..418b428cc16 100644
--- a/ports/geckolib/gecko_bindings/structs_release.rs
+++ b/ports/geckolib/gecko_bindings/structs_release.rs
@@ -5129,11 +5129,24 @@ pub type nsStyleUnion = nsStyleCoord_h_unnamed_18;
  * the unit is a must before asking for the value in any particular
  * form.
  */
+ /** <div rustbindgen private accessor="unsafe"></div> */
 #[repr(C)]
 #[derive(Debug)]
 pub struct nsStyleCoord {
-    pub mUnit: nsStyleUnit,
-    pub mValue: nsStyleUnion,
+    mUnit: nsStyleUnit,
+    mValue: nsStyleUnion,
+}
+impl nsStyleCoord {
+    #[inline]
+    pub unsafe fn get_mUnit(&self) -> &nsStyleUnit { &self.mUnit }
+    pub unsafe fn get_mUnit_mut(&mut self) -> &mut nsStyleUnit {
+        &mut self.mUnit
+    }
+    #[inline]
+    pub unsafe fn get_mValue(&self) -> &nsStyleUnion { &self.mValue }
+    pub unsafe fn get_mValue_mut(&mut self) -> &mut nsStyleUnion {
+        &mut self.mValue
+    }
 }
 #[repr(C)]
 #[derive(Debug, Copy)]
@@ -5174,11 +5187,26 @@ fn bindgen_test_layout_nsStyleCoord() {
  * This is commonly used to hold the widths of the borders, margins,
  * or paddings of a box.
  */
+ /** <div rustbindgen private accessor="unsafe"></div> */
 #[repr(C)]
 #[derive(Debug)]
 pub struct nsStyleSides {
-    pub mUnits: [nsStyleUnit; 4usize],
-    pub mValues: [nsStyleUnion; 4usize],
+    mUnits: [nsStyleUnit; 4usize],
+    mValues: [nsStyleUnion; 4usize],
+}
+impl nsStyleSides {
+    #[inline]
+    pub unsafe fn get_mUnits(&self) -> &[nsStyleUnit; 4usize] { &self.mUnits }
+    pub unsafe fn get_mUnits_mut(&mut self) -> &mut [nsStyleUnit; 4usize] {
+        &mut self.mUnits
+    }
+    #[inline]
+    pub unsafe fn get_mValues(&self) -> &[nsStyleUnion; 4usize] {
+        &self.mValues
+    }
+    pub unsafe fn get_mValues_mut(&mut self) -> &mut [nsStyleUnion; 4usize] {
+        &mut self.mValues
+    }
 }
 #[test]
 fn bindgen_test_layout_nsStyleSides() {
@@ -5190,11 +5218,26 @@ fn bindgen_test_layout_nsStyleSides() {
  * nsStyleCoord pairs.  This is used to hold the dimensions of the
  * corners of a box (for, e.g., border-radius and outline-radius).
  */
+ /** <div rustbindgen private accessor="unsafe"></div> */
 #[repr(C)]
 #[derive(Debug)]
 pub struct nsStyleCorners {
-    pub mUnits: [nsStyleUnit; 8usize],
-    pub mValues: [nsStyleUnion; 8usize],
+    mUnits: [nsStyleUnit; 8usize],
+    mValues: [nsStyleUnion; 8usize],
+}
+impl nsStyleCorners {
+    #[inline]
+    pub unsafe fn get_mUnits(&self) -> &[nsStyleUnit; 8usize] { &self.mUnits }
+    pub unsafe fn get_mUnits_mut(&mut self) -> &mut [nsStyleUnit; 8usize] {
+        &mut self.mUnits
+    }
+    #[inline]
+    pub unsafe fn get_mValues(&self) -> &[nsStyleUnion; 8usize] {
+        &self.mValues
+    }
+    pub unsafe fn get_mValues_mut(&mut self) -> &mut [nsStyleUnion; 8usize] {
+        &mut self.mValues
+    }
 }
 #[test]
 fn bindgen_test_layout_nsStyleCorners() {
diff --git a/ports/geckolib/gecko_bindings/sugar/ns_style_coord.rs b/ports/geckolib/gecko_bindings/sugar/ns_style_coord.rs
index 33dff1a705d..a13f08ea37b 100644
--- a/ports/geckolib/gecko_bindings/sugar/ns_style_coord.rs
+++ b/ports/geckolib/gecko_bindings/sugar/ns_style_coord.rs
@@ -3,24 +3,29 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use bindings::{Gecko_ResetStyleCoord, Gecko_SetStyleCoordCalcValue, Gecko_AddRefCalcArbitraryThread};
-use std::mem::transmute;
 use structs::{nsStyleCoord_Calc, nsStyleUnit, nsStyleUnion, nsStyleCoord, nsStyleSides, nsStyleCorners};
 use structs::{nsStyleCoord_CalcValue, nscoord};
 
 impl CoordData for nsStyleCoord {
     #[inline]
     fn unit(&self) -> nsStyleUnit {
-        self.mUnit
+        unsafe {
+            *self.get_mUnit()
+        }
     }
     #[inline]
     fn union(&self) -> nsStyleUnion {
-        self.mValue
+        unsafe {
+            *self.get_mValue()
+        }
     }
 }
 
 impl CoordDataMut for nsStyleCoord {
     unsafe fn values_mut(&mut self) -> (&mut nsStyleUnit, &mut nsStyleUnion) {
-        (&mut self.mUnit, &mut self.mValue)
+        let unit = self.get_mUnit_mut() as *mut _;
+        let value = self.get_mValue_mut() as *mut _;
+        (&mut *unit, &mut *value)
     }
 }
 
@@ -53,26 +58,36 @@ pub struct SidesDataMut<'a> {
 impl<'a> CoordData for SidesData<'a> {
     #[inline]
     fn unit(&self) -> nsStyleUnit {
-        self.sides.mUnits[self.index]
+        unsafe {
+            self.sides.get_mUnits()[self.index]
+        }
     }
     #[inline]
     fn union(&self) -> nsStyleUnion {
-        self.sides.mValues[self.index]
+        unsafe {
+            self.sides.get_mValues()[self.index]
+        }
     }
 }
 impl<'a> CoordData for SidesDataMut<'a> {
     #[inline]
     fn unit(&self) -> nsStyleUnit {
-        self.sides.mUnits[self.index]
+        unsafe {
+            self.sides.get_mUnits()[self.index]
+        }
     }
     #[inline]
     fn union(&self) -> nsStyleUnion {
-        self.sides.mValues[self.index]
+        unsafe {
+            self.sides.get_mValues()[self.index]
+        }
     }
 }
 impl<'a> CoordDataMut for SidesDataMut<'a> {
     unsafe fn values_mut(&mut self) -> (&mut nsStyleUnit, &mut nsStyleUnion) {
-        (&mut self.sides.mUnits[self.index], &mut self.sides.mValues[self.index])
+        let unit = &mut self.sides.get_mUnits_mut()[self.index] as *mut _;
+        let value = &mut self.sides.get_mValues_mut()[self.index] as *mut _;
+        (&mut *unit, &mut *value)
     }
 }
 
@@ -104,23 +119,33 @@ pub struct CornersDataMut<'a> {
 
 impl<'a> CoordData for CornersData<'a> {
     fn unit(&self) -> nsStyleUnit {
-        self.corners.mUnits[self.index]
+        unsafe {
+            self.corners.get_mUnits()[self.index]
+        }
     }
     fn union(&self) -> nsStyleUnion {
-        self.corners.mValues[self.index]
+        unsafe {
+            self.corners.get_mValues()[self.index]
+        }
     }
 }
 impl<'a> CoordData for CornersDataMut<'a> {
     fn unit(&self) -> nsStyleUnit {
-        self.corners.mUnits[self.index]
+        unsafe {
+            self.corners.get_mUnits()[self.index]
+        }
     }
     fn union(&self) -> nsStyleUnion {
-        self.corners.mValues[self.index]
+        unsafe {
+            self.corners.get_mValues()[self.index]
+        }
     }
 }
 impl<'a> CoordDataMut for CornersDataMut<'a> {
     unsafe fn values_mut(&mut self) -> (&mut nsStyleUnit, &mut nsStyleUnion) {
-        (&mut self.corners.mUnits[self.index], &mut self.corners.mValues[self.index])
+        let unit = &mut self.corners.get_mUnits_mut()[self.index] as *mut _;
+        let value = &mut self.corners.get_mValues_mut()[self.index] as *mut _;
+        (&mut *unit, &mut *value)
     }
 }
 
@@ -179,6 +204,13 @@ pub trait CoordDataMut : CoordData {
         }
     }
 
+    #[inline]
+    unsafe fn copy_from_unchecked<T: CoordData>(&mut self, other: &T) {
+            let (unit, union) = self.values_mut();
+            *unit = other.unit();
+            *union = other.union();
+    }
+
     #[inline(always)]
     fn set_value(&mut self, value: CoordDataValue) {
         use self::CoordDataValue::*;
@@ -254,7 +286,7 @@ pub trait CoordDataMut : CoordData {
     #[inline]
     unsafe fn as_calc_mut(&mut self) -> &mut nsStyleCoord_Calc {
         debug_assert!(self.unit() == nsStyleUnit::eStyleUnit_Calc);
-        transmute(*self.union().mPointer.as_mut() as *mut nsStyleCoord_Calc)
+        &mut *(*self.union().mPointer.as_mut() as *mut nsStyleCoord_Calc)
     }
 
     #[inline]
@@ -328,6 +360,6 @@ pub trait CoordData {
     #[inline]
     unsafe fn as_calc(&self) -> &nsStyleCoord_Calc {
         debug_assert!(self.unit() == nsStyleUnit::eStyleUnit_Calc);
-        transmute(*self.union().mPointer.as_ref() as *const nsStyleCoord_Calc)
+        &*(*self.union().mPointer.as_ref() as *const nsStyleCoord_Calc)
     }
 }