--- a/gfx/layers/ipc/WebRenderMessages.ipdlh
+++ b/gfx/layers/ipc/WebRenderMessages.ipdlh
@@ -110,17 +110,18 @@ struct OpAddRawFont {
 };
 
 struct OpDeleteFont {
   FontKey key;
 };
 
 struct OpAddFontInstance {
   MaybeFontInstanceOptions options;
-  MaybeFontInstancePlatformOptions platformOptions ;
+  MaybeFontInstancePlatformOptions platformOptions;
+  OffsetRange variations;
   FontInstanceKey instanceKey;
   FontKey fontKey;
   float glyphSize;
 };
 
 struct OpDeleteFontInstance {
   FontInstanceKey key;
 };

--- a/gfx/layers/wr/IpcResourceUpdateQueue.cpp
+++ b/gfx/layers/wr/IpcResourceUpdateQueue.cpp
@@ -277,21 +277,24 @@ IpcResourceUpdateQueue::DeleteFont(wr::F
   mUpdates.AppendElement(layers::OpDeleteFont(aKey));
 }
 
 void
 IpcResourceUpdateQueue::AddFontInstance(wr::FontInstanceKey aKey,
                                         wr::FontKey aFontKey,
                                         float aGlyphSize,
                                         const wr::FontInstanceOptions* aOptions,
-                                        const wr::FontInstancePlatformOptions* aPlatformOptions)
+                                        const wr::FontInstancePlatformOptions* aPlatformOptions,
+                                        Range<const gfx::FontVariation> aVariations)
 {
+  auto bytes = mWriter.WriteAsBytes(aVariations);
   mUpdates.AppendElement(layers::OpAddFontInstance(
     aOptions ? Some(*aOptions) : Nothing(),
     aPlatformOptions ? Some(*aPlatformOptions) : Nothing(),
+    bytes,
     aKey, aFontKey,
     aGlyphSize
   ));
 }
 
 void
 IpcResourceUpdateQueue::DeleteFontInstance(wr::FontInstanceKey aKey)
 {

--- a/gfx/layers/wr/IpcResourceUpdateQueue.h
+++ b/gfx/layers/wr/IpcResourceUpdateQueue.h
@@ -18,16 +18,22 @@ namespace wr {
 /// allocations and creates dedicated shmems for large allocations.
 class ShmSegmentsWriter {
 public:
   ShmSegmentsWriter(ipc::IShmemAllocator* aAllocator, size_t aChunkSize);
   ~ShmSegmentsWriter();
 
   layers::OffsetRange Write(Range<uint8_t> aBytes);
 
+  template<typename T>
+  layers::OffsetRange WriteAsBytes(Range<T> aValues)
+  {
+    return Write(Range<uint8_t>((uint8_t*)aValues.begin().get(), aValues.length() * sizeof(T)));
+  }
+
   void Flush(nsTArray<ipc::Shmem>& aSmallAllocs, nsTArray<ipc::Shmem>& aLargeAllocs);
 
   void Clear();
 
 protected:
   void AllocChunk();
   layers::OffsetRange AllocLargeChunk(size_t aSize);
 
@@ -90,17 +96,18 @@ public:
   void AddRawFont(wr::FontKey aKey, Range<uint8_t> aBytes, uint32_t aIndex);
 
   void DeleteFont(wr::FontKey aKey);
 
   void AddFontInstance(wr::FontInstanceKey aKey,
                        wr::FontKey aFontKey,
                        float aGlyphSize,
                        const wr::FontInstanceOptions* aOptions,
-                       const wr::FontInstancePlatformOptions* aPlatformOptions);
+                       const wr::FontInstancePlatformOptions* aPlatformOptions,
+                       Range<const gfx::FontVariation> aVariations);
 
   void DeleteFontInstance(wr::FontInstanceKey aKey);
 
   void Clear();
 
   void Flush(nsTArray<layers::OpUpdateResource>& aUpdates,
              nsTArray<ipc::Shmem>& aSmallAllocs,
              nsTArray<ipc::Shmem>& aLargeAllocs);

--- a/gfx/layers/wr/WebRenderBridgeChild.cpp
+++ b/gfx/layers/wr/WebRenderBridgeChild.cpp
@@ -308,17 +308,24 @@ WebRenderBridgeChild::GetFontKeyForScale
     resources.AddRawFont(fontKey, data.mFontBuffer.AsSlice(), data.mFontIndex);
 
     mFontKeys.Put(unscaled, fontKey);
   }
 
   instanceKey.mNamespace = GetNamespace();
   instanceKey.mHandle = GetNextResourceId();
 
-  resources.AddFontInstance(instanceKey, fontKey, aScaledFont->GetSize(), nullptr, nullptr);
+  Maybe<wr::FontInstanceOptions> options;
+  Maybe<wr::FontInstancePlatformOptions> platformOptions;
+  std::vector<FontVariation> variations;
+  aScaledFont->GetWRFontInstanceOptions(&options, &platformOptions, &variations);
+
+  resources.AddFontInstance(instanceKey, fontKey, aScaledFont->GetSize(),
+                            options.ptrOr(nullptr), platformOptions.ptrOr(nullptr),
+                            Range<const FontVariation>(variations.data(), variations.size()));
   UpdateResources(resources);
 
   mFontInstanceKeys.Put(aScaledFont, instanceKey);
 
   return instanceKey;
 }
 
 void

--- a/gfx/layers/wr/WebRenderBridgeParent.cpp
+++ b/gfx/layers/wr/WebRenderBridgeParent.cpp
@@ -292,20 +292,25 @@ WebRenderBridgeParent::UpdateResources(c
         if (!reader.Read(op.bytes(), bytes)) {
           return false;
         }
         aUpdates.AddRawFont(op.key(), bytes, op.fontIndex());
         break;
       }
       case OpUpdateResource::TOpAddFontInstance: {
         const auto& op = cmd.get_OpAddFontInstance();
+        wr::Vec_u8 variations;
+        if (!reader.Read(op.variations(), variations)) {
+            return false;
+        }
         aUpdates.AddFontInstance(op.instanceKey(), op.fontKey(),
                                  op.glyphSize(),
                                  op.options().ptrOr(nullptr),
-                                 op.platformOptions().ptrOr(nullptr));
+                                 op.platformOptions().ptrOr(nullptr),
+                                 variations);
         break;
       }
       case OpUpdateResource::TOpDeleteImage: {
         const auto& op = cmd.get_OpDeleteImage();
         aUpdates.DeleteImage(op.key());
         break;
       }
       case OpUpdateResource::TOpDeleteFont: {

--- a/gfx/webrender_bindings/WebRenderAPI.cpp
+++ b/gfx/webrender_bindings/WebRenderAPI.cpp
@@ -563,20 +563,22 @@ ResourceUpdateQueue::DeleteFont(wr::Font
   wr_resource_updates_delete_font(mUpdates, aKey);
 }
 
 void
 ResourceUpdateQueue::AddFontInstance(wr::FontInstanceKey aKey,
                                      wr::FontKey aFontKey,
                                      float aGlyphSize,
                                      const wr::FontInstanceOptions* aOptions,
-                                     const wr::FontInstancePlatformOptions* aPlatformOptions)
+                                     const wr::FontInstancePlatformOptions* aPlatformOptions,
+                                     wr::Vec_u8& aVariations)
 {
   wr_resource_updates_add_font_instance(mUpdates, aKey, aFontKey, aGlyphSize,
-                                        aOptions, aPlatformOptions);
+                                        aOptions, aPlatformOptions,
+                                        &aVariations.inner);
 }
 
 void
 ResourceUpdateQueue::DeleteFontInstance(wr::FontInstanceKey aKey)
 {
   wr_resource_updates_delete_font_instance(mUpdates, aKey);
 }
 

--- a/gfx/webrender_bindings/WebRenderAPI.h
+++ b/gfx/webrender_bindings/WebRenderAPI.h
@@ -96,17 +96,18 @@ public:
   void AddRawFont(wr::FontKey aKey, wr::Vec_u8& aBytes, uint32_t aIndex);
 
   void DeleteFont(wr::FontKey aKey);
 
   void AddFontInstance(wr::FontInstanceKey aKey,
                        wr::FontKey aFontKey,
                        float aGlyphSize,
                        const wr::FontInstanceOptions* aOptions,
-                       const wr::FontInstancePlatformOptions* aPlatformOptions);
+                       const wr::FontInstancePlatformOptions* aPlatformOptions,
+                       wr::Vec_u8& aVariations);
 
   void DeleteFontInstance(wr::FontInstanceKey aKey);
 
   void Clear();
 
   // Try to avoid using this when possible.
   wr::ResourceUpdates* Raw() { return mUpdates; }
 

--- a/gfx/webrender_bindings/src/bindings.rs
+++ b/gfx/webrender_bindings/src/bindings.rs
@@ -84,21 +84,32 @@ pub struct WrVecU8 {
 
 impl WrVecU8 {
     fn to_vec(self) -> Vec<u8> {
         unsafe { Vec::from_raw_parts(self.data, self.length, self.capacity) }
     }
 
     // Equivalent to `to_vec` but clears self instead of consuming the value.
     fn flush_into_vec(&mut self) -> Vec<u8> {
-        let vec = unsafe { Vec::from_raw_parts(self.data, self.length, self.capacity) };
+        self.convert_into_vec::<u8>()
+    }
+
+    // Like flush_into_vec, but also does an unsafe conversion to the desired type.
+    fn convert_into_vec<T>(&mut self) -> Vec<T> {
+        let vec = unsafe {
+            Vec::from_raw_parts(
+                self.data as *mut T,
+                self.length / mem::size_of::<T>(),
+                self.capacity / mem::size_of::<T>(),
+            )
+        };
         self.data = ptr::null_mut();
         self.length = 0;
         self.capacity = 0;
-        return vec;
+        vec
     }
 
     fn from_vec(mut v: Vec<u8>) -> WrVecU8 {
         let w = WrVecU8 {
             data: v.as_mut_ptr(),
             length: v.len(),
             capacity: v.capacity(),
         };
@@ -958,24 +969,26 @@ pub extern "C" fn wr_resource_updates_de
 
 #[no_mangle]
 pub extern "C" fn wr_resource_updates_add_font_instance(
     resources: &mut ResourceUpdates,
     key: WrFontInstanceKey,
     font_key: WrFontKey,
     glyph_size: f32,
     options: *const FontInstanceOptions,
-    platform_options: *const FontInstancePlatformOptions
+    platform_options: *const FontInstancePlatformOptions,
+    variations: &mut WrVecU8,
 ) {
     resources.add_font_instance(
         key,
         font_key,
         Au::from_f32_px(glyph_size),
         unsafe { options.as_ref().cloned() },
-        unsafe { platform_options.as_ref().cloned() }
+        unsafe { platform_options.as_ref().cloned() },
+        variations.convert_into_vec::<FontVariation>(),
     );
 }
 
 #[no_mangle]
 pub extern "C" fn wr_resource_updates_delete_font_instance(
     resources: &mut ResourceUpdates,
     key: WrFontInstanceKey
 ) {

--- a/gfx/webrender_bindings/webrender_ffi_generated.h
+++ b/gfx/webrender_bindings/webrender_ffi_generated.h
@@ -1217,17 +1217,18 @@ void wr_resource_updates_add_external_im
 WR_FUNC;
 
 WR_INLINE
 void wr_resource_updates_add_font_instance(ResourceUpdates *aResources,
                                            WrFontInstanceKey aKey,
                                            WrFontKey aFontKey,
                                            float aGlyphSize,
                                            const FontInstanceOptions *aOptions,
-                                           const FontInstancePlatformOptions *aPlatformOptions)
+                                           const FontInstancePlatformOptions *aPlatformOptions,
+                                           WrVecU8 *aVariations)
 WR_FUNC;
 
 WR_INLINE
 void wr_resource_updates_add_image(ResourceUpdates *aResources,
                                    WrImageKey aImageKey,
                                    const WrImageDescriptor *aDescriptor,
                                    WrVecU8 *aBytes)
 WR_FUNC;