diff --git a/dom/canvas/CanvasRenderingContext2D.cpp b/dom/canvas/CanvasRenderingContext2D.cpp
index e810c3e4f31e..f8eee7a9617a 100644
--- a/dom/canvas/CanvasRenderingContext2D.cpp
+++ b/dom/canvas/CanvasRenderingContext2D.cpp
@@ -2919,7 +2919,9 @@ static GeckoFontMetrics GetFontMetricsFromCanvas(void* aContext) {
             0.0f,
             0.0f};
   }
-  auto metrics = fontGroup->GetMetricsForCSSUnits(nsFontMetrics::eHorizontal);
+  auto metrics = fontGroup->GetMetricsForCSSUnits(
+      nsFontMetrics::eHorizontal, StyleQueryFontMetricsFlags::NEEDS_CH |
+                                      StyleQueryFontMetricsFlags::NEEDS_IC);
   return {Length::FromPixels(metrics.xHeight),
           Length::FromPixels(metrics.zeroWidth),
           Length::FromPixels(metrics.capHeight),
@@ -3037,8 +3039,9 @@ class CanvasUserSpaceMetrics final : public UserSpaceMetricsWithSize {
         return Gecko_GetFontMetrics(
             mPresContext, WritingMode(mCanvasStyle).IsVertical(),
             mCanvasStyle->StyleFont(), mCanvasStyle->StyleFont()->mFont.size,
-            /* aUseUserFontSet = */ true,
-            /* aRetrieveMathScales */ false);
+            StyleQueryFontMetricsFlags::USE_USER_FONT_SET |
+                StyleQueryFontMetricsFlags::NEEDS_CH |
+                StyleQueryFontMetricsFlags::NEEDS_IC);
       }
       case Type::Root:
         return GetFontMetrics(mPresContext->Document()->GetRootElement());
diff --git a/dom/svg/SVGAnimatedLength.cpp b/dom/svg/SVGAnimatedLength.cpp
index 5176bc5a1e63..0a570be640c6 100644
--- a/dom/svg/SVGAnimatedLength.cpp
+++ b/dom/svg/SVGAnimatedLength.cpp
@@ -133,8 +133,9 @@ GeckoFontMetrics UserSpaceMetrics::GetFontMetrics(const Element* aElement) {
           metrics = Gecko_GetFontMetrics(
               presContext, WritingMode(style).IsVertical(), style->StyleFont(),
               style->StyleFont()->mFont.size,
-              /* aUseUserFontSet = */ true,
-              /* aRetrieveMathScales */ false);
+              StyleQueryFontMetricsFlags::USE_USER_FONT_SET |
+                  StyleQueryFontMetricsFlags::NEEDS_CH |
+                  StyleQueryFontMetricsFlags::NEEDS_IC);
         });
   }
   return metrics;
@@ -290,8 +291,9 @@ GeckoFontMetrics NonSVGFrameUserSpaceMetrics::GetFontMetricsForType(
       return Gecko_GetFontMetrics(
           mFrame->PresContext(), mFrame->GetWritingMode().IsVertical(),
           mFrame->StyleFont(), mFrame->StyleFont()->mFont.size,
-          /* aUseUserFontSet = */ true,
-          /* aRetrieveMathScales */ false);
+          StyleQueryFontMetricsFlags::USE_USER_FONT_SET |
+              StyleQueryFontMetricsFlags::NEEDS_CH |
+              StyleQueryFontMetricsFlags::NEEDS_IC);
     case Type::Root:
       return GetFontMetrics(
           mFrame->PresContext()->Document()->GetRootElement());
diff --git a/gfx/thebes/gfxTextRun.cpp b/gfx/thebes/gfxTextRun.cpp
index 3730fca4f922..28d828fc701c 100644
--- a/gfx/thebes/gfxTextRun.cpp
+++ b/gfx/thebes/gfxTextRun.cpp
@@ -3940,7 +3940,7 @@ already_AddRefed<gfxFont> gfxFontGroup::WhichSystemFontSupportsChar(
 }
 
 gfxFont::Metrics gfxFontGroup::GetMetricsForCSSUnits(
-    gfxFont::Orientation aOrientation) {
+    gfxFont::Orientation aOrientation, StyleQueryFontMetricsFlags aFlags) {
   bool isFirst;
   RefPtr<gfxFont> font = GetFirstValidFont(0x20, nullptr, &isFirst);
   auto metrics = font->GetMetrics(aOrientation);
@@ -3948,7 +3948,8 @@ gfxFont::Metrics gfxFontGroup::GetMetricsForCSSUnits(
   // If the font we used to get metrics was not the first in the list,
   // or if it doesn't support the ZERO character, check for the font that
   // does support ZERO and use its metrics for the 'ch' unit.
-  if (!isFirst || !font->HasCharacter('0')) {
+  if ((aFlags & StyleQueryFontMetricsFlags::NEEDS_CH) &&
+      (!isFirst || !font->HasCharacter('0'))) {
     RefPtr<gfxFont> zeroFont = GetFirstValidFont('0');
     if (zeroFont != font) {
       const auto& zeroMetrics = zeroFont->GetMetrics(aOrientation);
@@ -3957,7 +3958,8 @@ gfxFont::Metrics gfxFontGroup::GetMetricsForCSSUnits(
   }
 
   // Likewise for the WATER ideograph character used as the basis for 'ic'.
-  if (!isFirst || !font->HasCharacter(0x6C34)) {
+  if ((aFlags & StyleQueryFontMetricsFlags::NEEDS_IC) &&
+      (!isFirst || !font->HasCharacter(0x6C34))) {
     RefPtr<gfxFont> icFont = GetFirstValidFont(0x6C34);
     if (icFont != font) {
       const auto& icMetrics = icFont->GetMetrics(aOrientation);
diff --git a/gfx/thebes/gfxTextRun.h b/gfx/thebes/gfxTextRun.h
index a527ad3d817a..7fbb5d8e7f67 100644
--- a/gfx/thebes/gfxTextRun.h
+++ b/gfx/thebes/gfxTextRun.h
@@ -1072,7 +1072,11 @@ class gfxFontGroup final : public gfxTextRunFactory {
   // to render specific characters, not simply the "first available" font.
   // https://drafts.csswg.org/css-values-4/#ch
   // https://drafts.csswg.org/css-values-4/#ic
-  gfxFont::Metrics GetMetricsForCSSUnits(gfxFont::Orientation aOrientation);
+  // Whether extra font resources may be loaded to resolve 'ch' and 'ic'
+  // depends on the corresponding flags passed by the caller.
+  gfxFont::Metrics GetMetricsForCSSUnits(
+      gfxFont::Orientation aOrientation,
+      mozilla::StyleQueryFontMetricsFlags aFlags);
 
  protected:
   friend class mozilla::PostTraversalTask;
diff --git a/layout/style/GeckoBindings.cpp b/layout/style/GeckoBindings.cpp
index 6a74c9fde3a0..53f26981b2c3 100644
--- a/layout/style/GeckoBindings.cpp
+++ b/layout/style/GeckoBindings.cpp
@@ -1285,8 +1285,8 @@ void AssertIsMainThreadOrServoFontMetricsLocked() {
 GeckoFontMetrics Gecko_GetFontMetrics(const nsPresContext* aPresContext,
                                       bool aIsVertical,
                                       const nsStyleFont* aFont,
-                                      Length aFontSize, bool aUseUserFontSet,
-                                      bool aRetrieveMathScales) {
+                                      Length aFontSize,
+                                      StyleQueryFontMetricsFlags flags) {
   AutoWriteLock guard(*sServoFFILock);
 
   // Getting font metrics can require some main thread only work to be
@@ -1302,13 +1302,14 @@ GeckoFontMetrics Gecko_GetFontMetrics(const nsPresContext* aPresContext,
 
   nsPresContext* presContext = const_cast<nsPresContext*>(aPresContext);
   RefPtr<nsFontMetrics> fm = nsLayoutUtils::GetMetricsFor(
-      presContext, aIsVertical, aFont, aFontSize, aUseUserFontSet);
+      presContext, aIsVertical, aFont, aFontSize,
+      bool(flags & StyleQueryFontMetricsFlags::USE_USER_FONT_SET));
   auto* fontGroup = fm->GetThebesFontGroup();
-  auto metrics = fontGroup->GetMetricsForCSSUnits(fm->Orientation());
+  auto metrics = fontGroup->GetMetricsForCSSUnits(fm->Orientation(), flags);
 
   float scriptPercentScaleDown = 0;
   float scriptScriptPercentScaleDown = 0;
-  if (aRetrieveMathScales) {
+  if (flags & StyleQueryFontMetricsFlags::NEEDS_MATH_SCALES) {
     RefPtr<gfxFont> font = fontGroup->GetFirstValidFont();
     if (font->TryGetMathTable()) {
       scriptPercentScaleDown = static_cast<float>(
diff --git a/layout/style/GeckoBindings.h b/layout/style/GeckoBindings.h
index c7cf59c2661c..ba4b3b641656 100644
--- a/layout/style/GeckoBindings.h
+++ b/layout/style/GeckoBindings.h
@@ -472,11 +472,9 @@ struct GeckoFontMetrics {
   float mScriptScriptPercentScaleDown;  // zero is invalid or means not found.
 };
 
-GeckoFontMetrics Gecko_GetFontMetrics(const nsPresContext*, bool is_vertical,
-                                      const nsStyleFont* font,
-                                      mozilla::Length font_size,
-                                      bool use_user_font_set,
-                                      bool retrieve_math_scales);
+GeckoFontMetrics Gecko_GetFontMetrics(
+    const nsPresContext*, bool is_vertical, const nsStyleFont* font,
+    mozilla::Length font_size, mozilla::StyleQueryFontMetricsFlags flags);
 
 mozilla::StyleSheet* Gecko_StyleSheet_Clone(const mozilla::StyleSheet* aSheet);
 
diff --git a/layout/style/ServoBindings.toml b/layout/style/ServoBindings.toml
index 0ae7445cfd44..ae62e3423cdf 100644
--- a/layout/style/ServoBindings.toml
+++ b/layout/style/ServoBindings.toml
@@ -634,7 +634,8 @@ cbindgen-types = [
     { gecko = "StyleInert", servo = "crate::values::computed::ui::Inert" },
     { gecko = "StyleMargin", servo = "crate::values::computed::length::Margin" },
     { gecko = "StyleGenericAnchorFunction", servo = "crate::values::generics::position::GenericAnchorFunction" },
-    { gecko = "StylePositionProperty", servo = "crate::values::computed::PositionProperty"},
+    { gecko = "StylePositionProperty", servo = "crate::values::computed::PositionProperty" },
+    { gecko = "StyleQueryFontMetricsFlags", servo = "crate::gecko::media_queries::QueryFontMetricsFlags" },
 ]
 
 mapped-generic-types = [
diff --git a/servo/components/style/gecko/media_queries.rs b/servo/components/style/gecko/media_queries.rs
index 59d5b1489413..645a54d55dab 100644
--- a/servo/components/style/gecko/media_queries.rs
+++ b/servo/components/style/gecko/media_queries.rs
@@ -29,6 +29,23 @@ use std::sync::atomic::{AtomicBool, AtomicU32, AtomicUsize, Ordering};
 use std::{cmp, fmt};
 use style_traits::{CSSPixel, DevicePixel};
 
+/// Flags for the query_font_metrics() function.
+#[repr(C)]
+pub struct QueryFontMetricsFlags(u8);
+
+bitflags! {
+    impl QueryFontMetricsFlags: u8 {
+        /// Should we use the user font set?
+        const USE_USER_FONT_SET = 1 << 0;
+        /// Does the caller need the `ch` unit (width of the ZERO glyph)?
+        const NEEDS_CH = 1 << 1;
+        /// Does the caller need the `ic` unit (width of the WATER ideograph)?
+        const NEEDS_IC = 1 << 2;
+        /// Does the caller need math scales to be retrieved?
+        const NEEDS_MATH_SCALES = 1 << 3;
+    }
+}
+
 /// The `Device` in Gecko wraps a pres context, has a default values computed,
 /// and contains all the viewport rule state.
 pub struct Device {
@@ -227,8 +244,7 @@ impl Device {
         vertical: bool,
         font: &crate::properties::style_structs::Font,
         base_size: Length,
-        in_media_query: bool,
-        retrieve_math_scales: bool,
+        flags: QueryFontMetricsFlags,
     ) -> FontMetrics {
         self.used_font_metrics.store(true, Ordering::Relaxed);
         let pc = match self.pres_context() {
@@ -241,9 +257,7 @@ impl Device {
                 vertical,
                 &**font,
                 base_size,
-                // we don't use the user font set in a media query
-                !in_media_query,
-                retrieve_math_scales,
+                flags,
             )
         };
         FontMetrics {
diff --git a/servo/components/style/properties/cascade.rs b/servo/components/style/properties/cascade.rs
index a2a957902940..2365a72aaf54 100644
--- a/servo/components/style/properties/cascade.rs
+++ b/servo/components/style/properties/cascade.rs
@@ -1355,6 +1355,8 @@ impl<'b> Cascade<'b> {
         }
 
         let (new_size, new_unconstrained_size) = {
+            use crate::gecko::media_queries::QueryFontMetricsFlags;
+
             let builder = &context.builder;
             let font = builder.get_font();
             let parent_font = builder.get_parent_font();
@@ -1376,7 +1378,7 @@ impl<'b> Cascade<'b> {
                 let font_metrics = context.query_font_metrics(
                     FontBaseSize::InheritedStyle,
                     FontMetricsOrientation::Horizontal,
-                    /* retrieve_math_scales = */ true,
+                    QueryFontMetricsFlags::NEEDS_MATH_SCALES,
                 );
                 scale_factor_for_math_depth_change(
                     parent_font.mMathDepth as i32,
diff --git a/servo/components/style/values/computed/font.rs b/servo/components/style/values/computed/font.rs
index d5dc33705083..3ce5235e3add 100644
--- a/servo/components/style/values/computed/font.rs
+++ b/servo/components/style/values/computed/font.rs
@@ -4,6 +4,7 @@
 
 //! Computed values for font properties
 
+use crate::gecko::media_queries::QueryFontMetricsFlags;
 use crate::parser::{Parse, ParserContext};
 use crate::values::animated::ToAnimatedValue;
 use crate::values::computed::{
@@ -802,13 +803,13 @@ impl ToComputedValue for specified::FontSizeAdjust {
     fn to_computed_value(&self, context: &Context) -> Self::ComputedValue {
         use crate::font_metrics::FontMetricsOrientation;
 
-        let font_metrics = |vertical| {
+        let font_metrics = |vertical, flags| {
             let orient = if vertical {
                 FontMetricsOrientation::MatchContextPreferVertical
             } else {
                 FontMetricsOrientation::Horizontal
             };
-            let metrics = context.query_font_metrics(FontBaseSize::CurrentStyle, orient, false);
+            let metrics = context.query_font_metrics(FontBaseSize::CurrentStyle, orient, flags);
             let font_size = context.style().get_font().clone_font_size().used_size.0;
             (metrics, font_size)
         };
@@ -817,13 +818,13 @@ impl ToComputedValue for specified::FontSizeAdjust {
         // returns the fallback value, or if that is negative, resolves using ascent instead
         // of the missing field (this is the fallback for cap-height).
         macro_rules! resolve {
-            ($basis:ident, $value:expr, $vertical:expr, $field:ident, $fallback:expr) => {{
+            ($basis:ident, $value:expr, $vertical:expr, $field:ident, $fallback:expr, $flags:expr) => {{
                 match $value {
                     specified::FontSizeAdjustFactor::Number(f) => {
                         FontSizeAdjust::$basis(f.to_computed_value(context))
                     },
                     specified::FontSizeAdjustFactor::FromFont => {
-                        let (metrics, font_size) = font_metrics($vertical);
+                        let (metrics, font_size) = font_metrics($vertical, $flags);
                         let ratio = if let Some(metric) = metrics.$field {
                             metric / font_size
                         } else if $fallback >= 0.0 {
@@ -843,13 +844,21 @@ impl ToComputedValue for specified::FontSizeAdjust {
 
         match *self {
             Self::None => FontSizeAdjust::None,
-            Self::ExHeight(val) => resolve!(ExHeight, val, false, x_height, 0.5),
-            Self::CapHeight(val) => {
-                resolve!(CapHeight, val, false, cap_height, -1.0 /* fall back to ascent */)
+            Self::ExHeight(val) => {
+                resolve!(ExHeight, val, false, x_height, 0.5, QueryFontMetricsFlags::empty())
+            },
+            Self::CapHeight(val) => {
+                resolve!(CapHeight, val, false, cap_height, -1.0 /* fall back to ascent */, QueryFontMetricsFlags::empty())
+            },
+            Self::ChWidth(val) => {
+                resolve!(ChWidth, val, false, zero_advance_measure, 0.5, QueryFontMetricsFlags::NEEDS_CH)
+            },
+            Self::IcWidth(val) => {
+                resolve!(IcWidth, val, false, ic_width, 1.0, QueryFontMetricsFlags::NEEDS_IC)
+            },
+            Self::IcHeight(val) => {
+                resolve!(IcHeight, val, true, ic_width, 1.0, QueryFontMetricsFlags::NEEDS_IC)
             },
-            Self::ChWidth(val) => resolve!(ChWidth, val, false, zero_advance_measure, 0.5),
-            Self::IcWidth(val) => resolve!(IcWidth, val, false, ic_width, 1.0),
-            Self::IcHeight(val) => resolve!(IcHeight, val, true, ic_width, 1.0),
         }
     }
 
diff --git a/servo/components/style/values/computed/mod.rs b/servo/components/style/values/computed/mod.rs
index 9caa30037f08..028d89da0a7e 100644
--- a/servo/components/style/values/computed/mod.rs
+++ b/servo/components/style/values/computed/mod.rs
@@ -18,6 +18,7 @@ use crate::computed_value_flags::ComputedValueFlags;
 use crate::context::QuirksMode;
 use crate::custom_properties::ComputedCustomProperties;
 use crate::font_metrics::{FontMetrics, FontMetricsOrientation};
+use crate::gecko::media_queries::QueryFontMetricsFlags;
 use crate::media_queries::Device;
 #[cfg(feature = "gecko")]
 use crate::properties;
@@ -363,7 +364,7 @@ impl<'a> Context<'a> {
         &self,
         base_size: FontBaseSize,
         orientation: FontMetricsOrientation,
-        retrieve_math_scales: bool,
+        mut flags: QueryFontMetricsFlags,
     ) -> FontMetrics {
         if self.for_non_inherited_property {
             self.rule_cache_conditions.borrow_mut().set_uncacheable();
@@ -390,12 +391,14 @@ impl<'a> Context<'a> {
             FontMetricsOrientation::MatchContextPreferVertical => wm.is_text_vertical(),
             FontMetricsOrientation::Horizontal => false,
         };
+        if !self.in_media_or_container_query() {
+            flags |= QueryFontMetricsFlags::USE_USER_FONT_SET
+        }
         self.device().query_font_metrics(
             vertical,
             font,
             size,
-            self.in_media_or_container_query(),
-            retrieve_math_scales,
+            flags,
         )
     }
 
diff --git a/servo/components/style/values/specified/length.rs b/servo/components/style/values/specified/length.rs
index cc11be9cc0f2..031e72ef4b77 100644
--- a/servo/components/style/values/specified/length.rs
+++ b/servo/components/style/values/specified/length.rs
@@ -9,6 +9,7 @@
 use super::{AllowQuirks, Number, Percentage, ToComputedValue};
 use crate::computed_value_flags::ComputedValueFlags;
 use crate::font_metrics::{FontMetrics, FontMetricsOrientation};
+use crate::gecko::media_queries::QueryFontMetricsFlags;
 #[cfg(feature = "gecko")]
 use crate::gecko_bindings::structs::GeckoFontMetrics;
 use crate::parser::{Parse, ParserContext};
@@ -249,9 +250,13 @@ impl FontRelativeLength {
             context: &Context,
             base_size: FontBaseSize,
             orientation: FontMetricsOrientation,
+            flags: QueryFontMetricsFlags,
         ) -> FontMetrics {
-            let retrieve_math_scales = false;
-            context.query_font_metrics(base_size, orientation, retrieve_math_scales)
+            context.query_font_metrics(
+                base_size,
+                orientation,
+                flags,
+            )
         }
 
         let reference_font_size = base_size.resolve(context);
@@ -268,8 +273,12 @@ impl FontRelativeLength {
             },
             Self::Ex(length) => {
                 // The x-height is an intrinsically horizontal metric.
-                let metrics =
-                    query_font_metrics(context, base_size, FontMetricsOrientation::Horizontal);
+                let metrics = query_font_metrics(
+                    context,
+                    base_size,
+                    FontMetricsOrientation::Horizontal,
+                    QueryFontMetricsFlags::empty(),
+                );
                 let reference_size = metrics.x_height.unwrap_or_else(|| {
                     // https://drafts.csswg.org/css-values/#ex
                     //
@@ -295,6 +304,7 @@ impl FontRelativeLength {
                     context,
                     base_size,
                     FontMetricsOrientation::MatchContextPreferHorizontal,
+                    QueryFontMetricsFlags::NEEDS_CH,
                 );
                 let reference_size = metrics.zero_advance_measure.unwrap_or_else(|| {
                     // https://drafts.csswg.org/css-values/#ch
@@ -319,8 +329,12 @@ impl FontRelativeLength {
                 (reference_size, length)
             },
             Self::Cap(length) => {
-                let metrics =
-                    query_font_metrics(context, base_size, FontMetricsOrientation::Horizontal);
+                let metrics = query_font_metrics(
+                    context,
+                    base_size,
+                    FontMetricsOrientation::Horizontal,
+                    QueryFontMetricsFlags::empty(),
+                );
                 let reference_size = metrics.cap_height.unwrap_or_else(|| {
                     // https://drafts.csswg.org/css-values/#cap
                     //
@@ -337,6 +351,7 @@ impl FontRelativeLength {
                     context,
                     base_size,
                     FontMetricsOrientation::MatchContextPreferVertical,
+                    QueryFontMetricsFlags::NEEDS_IC,
                 );
                 let reference_size = metrics.ic_width.unwrap_or_else(|| {
                     // https://drafts.csswg.org/css-values/#ic
diff --git a/servo/ports/geckolib/cbindgen.toml b/servo/ports/geckolib/cbindgen.toml
index 724d34e8c5ce..4ff50908d4b5 100644
--- a/servo/ports/geckolib/cbindgen.toml
+++ b/servo/ports/geckolib/cbindgen.toml
@@ -331,6 +331,7 @@ include = [
   "Margin",
   "PositionProperty",
   "PhysicalAxis",
+  "QueryFontMetricsFlags",
 ]
 item_types = [
   "enums",