diff --git a/components/style/gecko/url.rs b/components/style/gecko/url.rs
index ac7c9359b00..00f4ed8266b 100644
--- a/components/style/gecko/url.rs
+++ b/components/style/gecko/url.rs
@@ -285,14 +285,15 @@ impl SpecifiedImageUrl {
 
     /// Provides an alternate method for parsing that associates the URL
     /// with anonymous CORS headers.
-    pub fn parse_with_cors_anonymous<'i, 't>(
+    pub fn parse_with_cors_mode<'i, 't>(
         context: &ParserContext,
         input: &mut Parser<'i, 't>,
+        cors_mode: CorsMode,
     ) -> Result<Self, ParseError<'i>> {
         Ok(SpecifiedImageUrl(SpecifiedUrl::parse_with_cors_mode(
             context,
             input,
-            CorsMode::Anonymous,
+            cors_mode,
         )?))
     }
 }
diff --git a/components/style/values/computed/image.rs b/components/style/values/computed/image.rs
index 4eda2e91e21..6f609bdf6fa 100644
--- a/components/style/values/computed/image.rs
+++ b/components/style/values/computed/image.rs
@@ -15,7 +15,7 @@ use crate::values::computed::NumberOrPercentage;
 use crate::values::computed::{Angle, Color, Context};
 use crate::values::computed::{
     AngleOrPercentage, LengthPercentage, NonNegativeLength, NonNegativeLengthPercentage,
-    ToComputedValue,
+    ToComputedValue, Resolution,
 };
 use crate::values::generics::image::{self as generic, GradientCompatMode};
 use crate::values::specified::image::LineDirection as SpecifiedLineDirection;
@@ -26,7 +26,7 @@ use style_traits::{CssWriter, ToCss};
 
 /// Computed values for an image according to CSS-IMAGES.
 /// <https://drafts.csswg.org/css-images/#image-values>
-pub type Image = generic::GenericImage<Gradient, MozImageRect, ComputedImageUrl, Color, Percentage>;
+pub type Image = generic::GenericImage<Gradient, MozImageRect, ComputedImageUrl, Color, Percentage, Resolution>;
 
 /// Computed values for a CSS gradient.
 /// <https://drafts.csswg.org/css-images/#gradients>
diff --git a/components/style/values/computed/resolution.rs b/components/style/values/computed/resolution.rs
index c08fe2be1a3..72580635b81 100644
--- a/components/style/values/computed/resolution.rs
+++ b/components/style/values/computed/resolution.rs
@@ -13,6 +13,8 @@ use std::fmt::{self, Write};
 use style_traits::{CssWriter, ToCss};
 
 /// A computed `<resolution>`.
+#[repr(C)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToResolvedValue, ToShmem)]
 pub struct Resolution(CSSFloat);
 
 impl Resolution {
diff --git a/components/style/values/generics/image.rs b/components/style/values/generics/image.rs
index f92eca8ae2f..ff6498d668a 100644
--- a/components/style/values/generics/image.rs
+++ b/components/style/values/generics/image.rs
@@ -22,7 +22,7 @@ use style_traits::{CssWriter, ToCss};
     Clone, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToComputedValue, ToResolvedValue, ToShmem,
 )]
 #[repr(C, u8)]
-pub enum GenericImage<G, MozImageRect, ImageUrl, Color, Percentage> {
+pub enum GenericImage<G, MozImageRect, ImageUrl, Color, Percentage, Resolution> {
     /// `none` variant.
     None,
     /// A `<url()>` image.
@@ -51,6 +51,9 @@ pub enum GenericImage<G, MozImageRect, ImageUrl, Color, Percentage> {
     /// and store images directly inside of cross-fade instead of
     /// boxing them there.
     CrossFade(Box<GenericCrossFade<Self, Color, Percentage>>),
+
+    /// An `image-set()` function.
+    ImageSet(Box<GenericImageSet<Self, Resolution>>),
 }
 
 pub use self::GenericImage as Image;
@@ -135,6 +138,36 @@ pub use self::GenericCrossFade as CrossFade;
 pub use self::GenericCrossFadeElement as CrossFadeElement;
 pub use self::GenericCrossFadeImage as CrossFadeImage;
 
+/// https://drafts.csswg.org/css-images-4/#image-set-notation
+#[css(comma, function = "image-set")]
+#[derive(
+    Clone, Debug, MallocSizeOf, PartialEq, ToResolvedValue, ToShmem, ToCss, ToComputedValue,
+)]
+#[repr(C)]
+pub struct GenericImageSet<Image, Resolution> {
+    /// All of the image and resolution pairs.
+    #[css(iterable)]
+    pub items: crate::OwnedSlice<GenericImageSetItem<Image, Resolution>>,
+}
+
+/// An optional percent and a cross fade image.
+#[derive(
+    Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToResolvedValue, ToShmem, ToCss,
+)]
+#[repr(C)]
+pub struct GenericImageSetItem<Image, Resolution> {
+    /// `<image>`. `<string>` is converted to `Image::Url` at parse time.
+    pub image: Image,
+    /// The `<resolution>`.
+    ///
+    /// TODO: Skip serialization if it is 1x.
+    pub resolution: Resolution,
+    // TODO: type() function.
+}
+
+pub use self::GenericImageSet as ImageSet;
+pub use self::GenericImageSetItem as ImageSetItem;
+
 /// A CSS gradient.
 /// <https://drafts.csswg.org/css-images/#gradients>
 #[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToResolvedValue, ToShmem)]
@@ -377,26 +410,23 @@ pub struct GenericMozImageRect<NumberOrPercentage, MozImageRectUrl> {
 
 pub use self::GenericMozImageRect as MozImageRect;
 
-impl<G, R, U, C, P> fmt::Debug for Image<G, R, U, C, P>
+impl<G, R, U, C, P, Resolution> fmt::Debug for Image<G, R, U, C, P, Resolution>
 where
-    G: ToCss,
-    R: ToCss,
-    U: ToCss,
-    C: ToCss,
-    P: ToCss,
+    Image<G, R, U, C, P, Resolution>: ToCss,
 {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         self.to_css(&mut CssWriter::new(f))
     }
 }
 
-impl<G, R, U, C, P> ToCss for Image<G, R, U, C, P>
+impl<G, R, U, C, P, Resolution> ToCss for Image<G, R, U, C, P, Resolution>
 where
     G: ToCss,
     R: ToCss,
     U: ToCss,
     C: ToCss,
     P: ToCss,
+    Resolution: ToCss,
 {
     fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
     where
@@ -415,6 +445,7 @@ where
                 serialize_atom_identifier(selector, dest)?;
                 dest.write_str(")")
             },
+            Image::ImageSet(ref is) => is.to_css(dest),
             Image::CrossFade(ref cf) => cf.to_css(dest),
         }
     }
diff --git a/components/style/values/specified/image.rs b/components/style/values/specified/image.rs
index 86b01cb5a31..1a0711231b3 100644
--- a/components/style/values/specified/image.rs
+++ b/components/style/values/specified/image.rs
@@ -9,6 +9,7 @@
 
 use crate::custom_properties::SpecifiedValue;
 use crate::parser::{Parse, ParserContext};
+use crate::stylesheets::CorsMode;
 use crate::values::generics::image::PaintWorklet;
 use crate::values::generics::image::{
     self as generic, Circle, Ellipse, GradientCompatMode, ShapeExtent,
@@ -20,7 +21,7 @@ use crate::values::specified::position::{Position, PositionComponent, Side};
 use crate::values::specified::url::SpecifiedImageUrl;
 use crate::values::specified::{
     Angle, AngleOrPercentage, Color, Length, LengthPercentage, NonNegativeLength,
-    NonNegativeLengthPercentage,
+    NonNegativeLengthPercentage, Resolution
 };
 use crate::values::specified::{Number, NumberOrPercentage, Percentage};
 use crate::Atom;
@@ -35,7 +36,7 @@ use style_traits::{SpecifiedValueInfo, StyleParseErrorKind, ToCss};
 
 /// Specified values for an image according to CSS-IMAGES.
 /// <https://drafts.csswg.org/css-images/#image-values>
-pub type Image = generic::Image<Gradient, MozImageRect, SpecifiedImageUrl, Color, Percentage>;
+pub type Image = generic::Image<Gradient, MozImageRect, SpecifiedImageUrl, Color, Percentage, Resolution>;
 
 /// Specified values for a CSS gradient.
 /// <https://drafts.csswg.org/css-images/#gradients>
@@ -61,6 +62,12 @@ pub type CrossFadeImage = generic::CrossFadeImage<Image, Color>;
 /// A specified percentage or nothing.
 pub type PercentOrNone = generic::PercentOrNone<Percentage>;
 
+/// `image-set()`
+pub type ImageSet = generic::ImageSet<Image, Resolution>;
+
+/// Each of the arguments to `image-set()`
+pub type ImageSetItem = generic::ImageSetItem<Image, Resolution>;
+
 type LengthPercentageItemList = crate::OwnedSlice<generic::GradientItem<Color, LengthPercentage>>;
 
 #[cfg(feature = "gecko")]
@@ -73,6 +80,16 @@ fn cross_fade_enabled() -> bool {
     false
 }
 
+#[cfg(feature = "gecko")]
+fn image_set_enabled() -> bool {
+    static_prefs::pref!("layout.css.image-set.enabled")
+}
+
+#[cfg(feature = "servo")]
+fn image_set_enabled() -> bool {
+    false
+}
+
 impl SpecifiedValueInfo for Gradient {
     const SUPPORTED_TYPES: u8 = CssType::GRADIENT;
 
@@ -110,6 +127,16 @@ impl<Image, Color, Percentage> SpecifiedValueInfo for generic::CrossFade<Image,
     }
 }
 
+impl<Image, Resolution> SpecifiedValueInfo for generic::ImageSet<Image, Resolution> {
+    const SUPPORTED_TYPES: u8 = 0;
+
+    fn collect_completion_keywords(f: KeywordsCollectFn) {
+        if image_set_enabled() {
+            f(&["image-set"]);
+        }
+    }
+}
+
 /// A specified gradient line direction.
 ///
 /// FIXME(emilio): This should be generic over Angle.
@@ -152,18 +179,33 @@ impl Parse for Image {
     fn parse<'i, 't>(
         context: &ParserContext,
         input: &mut Parser<'i, 't>,
+    ) -> Result<Image, ParseError<'i>> {
+        Image::parse_with_cors_mode(context, input, CorsMode::None)
+    }
+}
+
+impl Image {
+    fn parse_with_cors_mode<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+        cors_mode: CorsMode,
     ) -> Result<Image, ParseError<'i>> {
         if input.try_parse(|i| i.expect_ident_matching("none")).is_ok() {
             return Ok(generic::Image::None);
         }
-        if let Ok(url) = input.try_parse(|input| SpecifiedImageUrl::parse(context, input)) {
+        if let Ok(url) = input.try_parse(|input| SpecifiedImageUrl::parse_with_cors_mode(context, input, cors_mode)) {
             return Ok(generic::Image::Url(url));
         }
         if let Ok(gradient) = input.try_parse(|i| Gradient::parse(context, i)) {
             return Ok(generic::Image::Gradient(Box::new(gradient)));
         }
+        if image_set_enabled() {
+            if let Ok(is) = input.try_parse(|input| ImageSet::parse(context, input, cors_mode)) {
+                return Ok(generic::Image::ImageSet(Box::new(is)));
+            }
+        }
         if cross_fade_enabled() {
-            if let Ok(cf) = input.try_parse(|input| CrossFade::parse(context, input)) {
+            if let Ok(cf) = input.try_parse(|input| CrossFade::parse(context, input, cors_mode)) {
                 return Ok(generic::Image::CrossFade(Box::new(cf)));
             }
         }
@@ -175,7 +217,7 @@ impl Parse for Image {
         }
         #[cfg(feature = "gecko")]
         {
-            if let Ok(image_rect) = input.try_parse(|input| MozImageRect::parse(context, input)) {
+            if let Ok(image_rect) = input.try_parse(|input| MozImageRect::parse(context, input, cors_mode)) {
                 return Ok(generic::Image::Rect(Box::new(image_rect)));
             }
             Ok(generic::Image::Element(Image::parse_element(input)?))
@@ -214,40 +256,37 @@ impl Image {
         context: &ParserContext,
         input: &mut Parser<'i, 't>,
     ) -> Result<Image, ParseError<'i>> {
-        if let Ok(url) =
-            input.try_parse(|input| SpecifiedImageUrl::parse_with_cors_anonymous(context, input))
-        {
-            return Ok(generic::Image::Url(url));
-        }
-        Self::parse(context, input)
+        Self::parse_with_cors_mode(context, input, CorsMode::Anonymous)
     }
 }
 
-impl Parse for CrossFade {
+impl CrossFade {
     /// cross-fade() = cross-fade( <cf-image># )
     fn parse<'i, 't>(
         context: &ParserContext,
         input: &mut Parser<'i, 't>,
+        cors_mode: CorsMode,
     ) -> Result<Self, ParseError<'i>> {
         input.expect_function_matching("cross-fade")?;
         let elements = input.parse_nested_block(|input| {
-            input.parse_comma_separated(|input| CrossFadeElement::parse(context, input))
+            input.parse_comma_separated(|input| CrossFadeElement::parse(context, input, cors_mode))
         })?;
         let elements = crate::OwnedSlice::from(elements);
         Ok(Self { elements })
     }
 }
 
-impl Parse for CrossFadeElement {
+impl CrossFadeElement {
     /// <cf-image> = <percentage>? && [ <image> | <color> ]
     fn parse<'i, 't>(
         context: &ParserContext,
         input: &mut Parser<'i, 't>,
+        cors_mode: CorsMode,
     ) -> Result<Self, ParseError<'i>> {
         // Try and parse a leading percent sign.
         let mut percent = PercentOrNone::parse_or_none(context, input);
         // Parse the image
-        let image = CrossFadeImage::parse(context, input)?;
+        let image = CrossFadeImage::parse(context, input, cors_mode)?;
         // Try and parse a trailing percent sign.
         if percent == PercentOrNone::None {
             percent = PercentOrNone::parse_or_none(context, input);
@@ -274,6 +313,40 @@ impl PercentOrNone {
     }
 }
 
+impl ImageSet {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+        cors_mode: CorsMode,
+    ) -> Result<Self, ParseError<'i>> {
+        input.expect_function_matching("image-set")?;
+        let items = input.parse_nested_block(|input| {
+            input.parse_comma_separated(|input| ImageSetItem::parse(context, input, cors_mode))
+        })?;
+        Ok(Self {
+            items: items.into()
+        })
+    }
+}
+
+impl ImageSetItem {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+        cors_mode: CorsMode,
+    ) -> Result<Self, ParseError<'i>> {
+        let image = match input.try_parse(|i| i.expect_url_or_string()) {
+            Ok(url) => Image::Url(SpecifiedImageUrl::parse_from_string(url.as_ref().into(), context, cors_mode)),
+            Err(..) => Image::parse(context, input)?,
+        };
+        let resolution = input.try_parse(|input| Resolution::parse(context, input)).unwrap_or(Resolution::X(1.0));
+        Ok(Self {
+            image,
+            resolution,
+        })
+    }
+}
+
 impl Parse for Gradient {
     fn parse<'i, 't>(
         context: &ParserContext,
@@ -1043,11 +1116,12 @@ impl Parse for PaintWorklet {
     }
 }
 
-impl Parse for MozImageRect {
+impl MozImageRect {
     #[cfg(not(feature = "gecko"))]
     fn parse<'i, 't>(
         _context: &ParserContext,
         input: &mut Parser<'i, 't>,
+        _cors_mode: CorsMode,
     ) -> Result<Self, ParseError<'i>> {
         Err(input.new_error_for_next_token())
     }
@@ -1056,6 +1130,7 @@ impl Parse for MozImageRect {
     fn parse<'i, 't>(
         context: &ParserContext,
         input: &mut Parser<'i, 't>,
+        cors_mode: CorsMode,
     ) -> Result<Self, ParseError<'i>> {
         input.try_parse(|i| i.expect_function_matching("-moz-image-rect"))?;
         input.parse_nested_block(|i| {
@@ -1063,7 +1138,7 @@ impl Parse for MozImageRect {
             let url = SpecifiedImageUrl::parse_from_string(
                 string.as_ref().to_owned(),
                 context,
-                crate::stylesheets::CorsMode::None,
+                cors_mode,
             );
             i.expect_comma()?;
             let top = NumberOrPercentage::parse_non_negative(context, i)?;
diff --git a/components/style/values/specified/resolution.rs b/components/style/values/specified/resolution.rs
index f8854226b53..e8674cffaaa 100644
--- a/components/style/values/specified/resolution.rs
+++ b/components/style/values/specified/resolution.rs
@@ -12,7 +12,7 @@ use cssparser::{Parser, Token};
 use style_traits::{ParseError, StyleParseErrorKind};
 
 /// A specified resolution.
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss, ToShmem)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss, ToShmem, SpecifiedValueInfo)]
 pub enum Resolution {
     /// Dots per inch.
     #[css(dimension)]