diff --git a/components/style/gecko/media_queries.rs b/components/style/gecko/media_queries.rs
index 27d8a5f6c62..63ccf68a541 100644
--- a/components/style/gecko/media_queries.rs
+++ b/components/style/gecko/media_queries.rs
@@ -186,6 +186,11 @@ impl Device {
     pub fn default_background_color(&self) -> RGBA {
         convert_nscolor_to_rgba(self.pres_context().mBackgroundColor)
     }
+
+    /// Applies text zoom to a font-size or line-height value (see nsStyleFont::ZoomText).
+    pub fn zoom_text(&self, size: Au) -> Au {
+        size.scale_by(self.pres_context().mEffectiveTextZoom)
+    }
 }
 
 /// A expression for gecko contains a reference to the media feature, the value
diff --git a/components/style/properties/gecko.mako.rs b/components/style/properties/gecko.mako.rs
index be27f6bcdd4..edf160a0a94 100644
--- a/components/style/properties/gecko.mako.rs
+++ b/components/style/properties/gecko.mako.rs
@@ -2231,9 +2231,6 @@ fn static_assert() {
         )
     }
 
-    // FIXME(bholley): Gecko has two different sizes, one of which (mSize) is the
-    // actual computed size, and the other of which (mFont.size) is the 'display
-    // size' which takes font zooming into account. We don't handle font zooming yet.
     pub fn set_font_size(&mut self, v: longhands::font_size::computed_value::T) {
         self.gecko.mSize = v.0;
         self.gecko.mScriptUnconstrainedSize = v.0;
diff --git a/components/style/properties/longhand/font.mako.rs b/components/style/properties/longhand/font.mako.rs
index f6b78a91749..f2f65e2dff0 100644
--- a/components/style/properties/longhand/font.mako.rs
+++ b/components/style/properties/longhand/font.mako.rs
@@ -830,17 +830,17 @@ ${helpers.single_keyword_system("font-variant-caps",
                     value.to_computed_value(base_size.resolve(context))
                 }
                 SpecifiedValue::Length(LengthOrPercentage::Length(ref l)) => {
-                    l.to_computed_value(context)
+                    context.maybe_zoom_text(l.to_computed_value(context))
                 }
                 SpecifiedValue::Length(LengthOrPercentage::Percentage(pc)) => {
                     base_size.resolve(context).scale_by(pc.0)
                 }
                 SpecifiedValue::Length(LengthOrPercentage::Calc(ref calc)) => {
-                    let calc = calc.to_computed_value(context);
+                    let calc = calc.to_computed_value_zoomed(context);
                     calc.to_used_value(Some(base_size.resolve(context))).unwrap()
                 }
                 SpecifiedValue::Keyword(ref key, fraction) => {
-                    key.to_computed_value(context).scale_by(fraction)
+                    context.maybe_zoom_text(key.to_computed_value(context).scale_by(fraction))
                 }
                 SpecifiedValue::Smaller => {
                     FontRelativeLength::Em(1. / LARGER_FONT_SIZE_RATIO)
@@ -960,7 +960,7 @@ ${helpers.single_keyword_system("font-variant-caps",
                context.builder.get_font().gecko().mGenericID !=
                context.builder.get_parent_font().gecko().mGenericID {
                 if let Some((kw, ratio)) = context.builder.font_size_keyword {
-                    computed = kw.to_computed_value(context).scale_by(ratio);
+                    computed = context.maybe_zoom_text(kw.to_computed_value(context).scale_by(ratio));
                 }
             }
         % endif
@@ -990,7 +990,7 @@ ${helpers.single_keyword_system("font-variant-caps",
         // changes using the font_size_keyword. We also need to do this to
         // handle mathml scriptlevel changes
         let kw_inherited_size = context.builder.font_size_keyword.map(|(kw, ratio)| {
-            SpecifiedValue::Keyword(kw, ratio).to_computed_value(context)
+            context.maybe_zoom_text(SpecifiedValue::Keyword(kw, ratio).to_computed_value(context))
         });
         let parent_kw;
         let device = context.builder.device;
@@ -1015,8 +1015,10 @@ ${helpers.single_keyword_system("font-variant-caps",
     pub fn cascade_initial_font_size(context: &mut Context) {
         // font-size's default ("medium") does not always
         // compute to the same value and depends on the font
-        let computed = longhands::font_size::get_initial_specified_value()
-                            .to_computed_value(context);
+        let computed = context.maybe_zoom_text(
+                            longhands::font_size::get_initial_specified_value()
+                                .to_computed_value(context)
+                        );
         context.builder.mutate_font().set_font_size(computed);
         % if product == "gecko":
             let device = context.builder.device;
diff --git a/components/style/values/computed/length.rs b/components/style/values/computed/length.rs
index 8682487f47d..29117a5cb8d 100644
--- a/components/style/values/computed/length.rs
+++ b/components/style/values/computed/length.rs
@@ -228,14 +228,14 @@ impl ToCss for CalcLengthOrPercentage {
     }
 }
 
-impl ToComputedValue for specified::CalcLengthOrPercentage {
-    type ComputedValue = CalcLengthOrPercentage;
-
-    fn to_computed_value(&self, context: &Context) -> CalcLengthOrPercentage {
+impl specified::CalcLengthOrPercentage {
+    /// Compute the value, zooming any absolute units by the zoom function.
+    fn to_computed_value_with_zoom<F>(&self, context: &Context, zoom_fn: F) -> CalcLengthOrPercentage
+        where F: Fn(Au) -> Au {
         let mut length = Au(0);
 
         if let Some(absolute) = self.absolute {
-            length += absolute;
+            length += zoom_fn(absolute);
         }
 
         for val in &[self.vw.map(ViewportPercentageLength::Vw),
@@ -263,6 +263,19 @@ impl ToComputedValue for specified::CalcLengthOrPercentage {
         }
     }
 
+    /// Compute font-size or line-height taking into account text-zoom if necessary.
+    pub fn to_computed_value_zoomed(&self, context: &Context) -> CalcLengthOrPercentage {
+        self.to_computed_value_with_zoom(context, |abs| context.maybe_zoom_text(abs))
+    }
+}
+
+impl ToComputedValue for specified::CalcLengthOrPercentage {
+    type ComputedValue = CalcLengthOrPercentage;
+
+    fn to_computed_value(&self, context: &Context) -> CalcLengthOrPercentage {
+        self.to_computed_value_with_zoom(context, |abs| abs)
+    }
+
     #[inline]
     fn from_computed_value(computed: &CalcLengthOrPercentage) -> Self {
         specified::CalcLengthOrPercentage {
diff --git a/components/style/values/computed/mod.rs b/components/style/values/computed/mod.rs
index 75dea7bf87b..d2b49ef5e22 100644
--- a/components/style/values/computed/mod.rs
+++ b/components/style/values/computed/mod.rs
@@ -132,6 +132,26 @@ impl<'a> Context<'a> {
     pub fn style(&self) -> &StyleBuilder {
         &self.builder
     }
+
+
+    /// Apply text-zoom if enabled
+    #[cfg(feature = "gecko")]
+    pub fn maybe_zoom_text(&self, size: Au) -> Au {
+        // We disable zoom for <svg:text> by unsetting the
+        // -x-text-zoom property, which leads to a false value
+        // in mAllowZoom
+        if self.style().get_font().gecko.mAllowZoom {
+            self.device().zoom_text(size)
+        } else {
+            size
+        }
+    }
+
+    /// (Servo doesn't do text-zoom)
+    #[cfg(feature = "servo")]
+    pub fn maybe_zoom_text(&self, size: Au) -> Au {
+        size
+    }
 }
 
 /// An iterator over a slice of computed values