diff --git a/src/components/gfx/display_list.rs b/src/components/gfx/display_list.rs
index 89d847938eb..acc94992d85 100644
--- a/src/components/gfx/display_list.rs
+++ b/src/components/gfx/display_list.rs
@@ -26,6 +26,7 @@ use libc::uintptr_t;
 use servo_net::image::base::Image;
 use servo_util::geometry::Au;
 use servo_util::range::Range;
+use std::fmt;
 use std::mem;
 use std::slice::Items;
 use style::computed_values::border_style;
@@ -638,23 +639,27 @@ impl DisplayItem {
             for _ in range(0, level) {
                 indent.push_str("| ")
             }
-            debug!("{}+ {}", indent, self.debug_str());
+            debug!("{}+ {}", indent, self);
             for child in self.children() {
                 child.debug_with_level(level + 1);
             }
     }
-
-    pub fn debug_str(&self) -> ~str {
-        let class = match *self {
-            SolidColorDisplayItemClass(_) => "SolidColor",
-            TextDisplayItemClass(_) => "Text",
-            ImageDisplayItemClass(_) => "Image",
-            BorderDisplayItemClass(_) => "Border",
-            LineDisplayItemClass(_) => "Line",
-            ClipDisplayItemClass(_) => "Clip",
-            PseudoDisplayItemClass(_) => "Pseudo",
-        };
-        format!("{} @ {} ({:x})", class, self.base().bounds, self.base().node.id())
-    }
 }
 
+impl fmt::Show for DisplayItem {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "{} @ {} ({:x})",
+            match *self {
+                SolidColorDisplayItemClass(_) => "SolidColor",
+                TextDisplayItemClass(_) => "Text",
+                ImageDisplayItemClass(_) => "Image",
+                BorderDisplayItemClass(_) => "Border",
+                LineDisplayItemClass(_) => "Line",
+                ClipDisplayItemClass(_) => "Clip",
+                PseudoDisplayItemClass(_) => "Pseudo",
+            },
+            self.base().bounds,
+            self.base().node.id(),
+        )
+    }
+}
diff --git a/src/components/main/layout/block.rs b/src/components/main/layout/block.rs
index 1c56467e1c1..2f258c0eedf 100644
--- a/src/components/main/layout/block.rs
+++ b/src/components/main/layout/block.rs
@@ -38,6 +38,7 @@ use gfx::render_task::RenderLayer;
 use servo_msg::compositor_msg::{FixedPosition, LayerId, Scrollable};
 use servo_util::geometry::Au;
 use servo_util::geometry;
+use std::fmt;
 use std::mem;
 use std::num::Zero;
 use style::computed_values::{LPA_Auto, LPA_Length, LPA_Percentage, LPN_Length, LPN_None};
@@ -1690,22 +1691,23 @@ impl Flow for BlockFlow {
         LayerId(self.box_.node.id(), fragment_index)
     }
 
-    fn debug_str(&self) -> ~str {
-        let txt = if self.is_float() {
-            "FloatFlow: ".to_owned()
-        } else if self.is_root() {
-            "RootFlow: ".to_owned()
-        } else {
-            "BlockFlow: ".to_owned()
-        };
-        txt.append(self.box_.debug_str())
-    }
-
     fn is_absolute_containing_block(&self) -> bool {
         self.is_positioned()
     }
 }
 
+impl fmt::Show for BlockFlow {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if self.is_float() {
+            write!(f.buf, "FloatFlow: {}", self.box_)
+        } else if self.is_root() {
+            write!(f.buf, "RootFlow: {}", self.box_)
+        } else {
+            write!(f.buf, "BlockFlow: {}", self.box_)
+        }
+    }
+}
+
 /// The inputs for the widths-and-margins constraint equation.
 pub struct WidthConstraintInput {
     pub computed_width: MaybeAuto,
diff --git a/src/components/main/layout/box_.rs b/src/components/main/layout/box_.rs
index b738006b822..416e9400106 100644
--- a/src/components/main/layout/box_.rs
+++ b/src/components/main/layout/box_.rs
@@ -38,6 +38,7 @@ use servo_util::namespace;
 use servo_util::smallvec::SmallVec;
 use servo_util::str::is_whitespace;
 use std::cast;
+use std::fmt;
 use std::from_str::FromStr;
 use std::iter::AdditiveIterator;
 use std::mem;
@@ -838,10 +839,10 @@ impl Box {
         // Box position wrt to the owning flow.
         let box_bounds = self.border_box;
         let absolute_box_bounds = box_bounds.translate(&flow_origin);
-        debug!("Box::build_display_list at rel={}, abs={}: {:s}",
+        debug!("Box::build_display_list at rel={}, abs={}: {}",
                box_bounds,
                absolute_box_bounds,
-               self.debug_str());
+               self);
         debug!("Box::build_display_list: dirty={}, flow_origin={}",
                layout_context.dirty,
                flow_origin);
@@ -1396,40 +1397,21 @@ impl Box {
         self.style().Box.get().overflow == overflow::hidden
     }
 
-    /// Returns a debugging string describing this box.
-    pub fn debug_str(&self) -> ~str {
-        let class_name = match self.specific {
-            GenericBox => "GenericBox",
-            IframeBox(_) => "IframeBox",
-            ImageBox(_) => "ImageBox",
-            ScannedTextBox(_) => "ScannedTextBox",
-            TableBox => "TableBox",
-            TableCellBox => "TableCellBox",
-            TableColumnBox(_) => "TableColumnBox",
-            TableRowBox => "TableRowBox",
-            TableWrapperBox => "TableWrapperBox",
-            UnscannedTextBox(_) => "UnscannedTextBox",
-        };
-
-        format!("({}{}{})",
-                class_name,
-                self.side_offsets_debug_string("bp", self.border_padding),
-                self.side_offsets_debug_string("m", self.margin))
-    }
-
     /// A helper function to return a debug string describing the side offsets for one of the rect
     /// box model properties (border, padding, or margin).
-    fn side_offsets_debug_string(&self, name: &str, value: SideOffsets2D<Au>) -> ~str {
-        let zero: SideOffsets2D<Au> = Zero::zero();
-        if value == zero {
-            return "".to_str()
-        }
-        format!(" {}{},{},{},{}",
+    fn side_offsets_debug_fmt(&self, name: &str,
+                              value: SideOffsets2D<Au>,
+                              f: &mut fmt::Formatter) -> fmt::Result {
+        if value.is_zero() {
+            Ok(())
+        } else {
+            write!(f.buf, "{}{},{},{},{}",
                 name,
                 value.top,
                 value.right,
                 value.bottom,
                 value.left)
+        }
     }
 
     /// Sends the size and position of this iframe box to the constellation. This is out of line to
@@ -1456,6 +1438,29 @@ impl Box {
     }
 }
 
+impl fmt::Show for Box {
+    /// Outputs a debugging string describing this box.
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        try!(write!(f.buf, "({} ",
+            match self.specific {
+                GenericBox => "GenericBox",
+                IframeBox(_) => "IframeBox",
+                ImageBox(_) => "ImageBox",
+                ScannedTextBox(_) => "ScannedTextBox",
+                TableBox => "TableBox",
+                TableCellBox => "TableCellBox",
+                TableColumnBox(_) => "TableColumnBox",
+                TableRowBox => "TableRowBox",
+                TableWrapperBox => "TableWrapperBox",
+                UnscannedTextBox(_) => "UnscannedTextBox",
+        }));
+        try!(self.side_offsets_debug_fmt("bp", self.border_padding, f));
+        try!(write!(f.buf, " "));
+        try!(self.side_offsets_debug_fmt("m", self.margin, f));
+        write!(f.buf, ")")
+    }
+}
+
 /// An object that accumulates display lists of child flows, applying a clipping rect if necessary.
 pub struct ChildDisplayListAccumulator {
     clip_display_item: Option<~ClipDisplayItem>,
diff --git a/src/components/main/layout/flow.rs b/src/components/main/layout/flow.rs
index 6be1e43adc6..7d79f4faf8f 100644
--- a/src/components/main/layout/flow.rs
+++ b/src/components/main/layout/flow.rs
@@ -55,6 +55,7 @@ use gfx::render_task::RenderLayer;
 use servo_msg::compositor_msg::LayerId;
 use servo_util::geometry::Au;
 use std::cast;
+use std::fmt;
 use std::iter::Zip;
 use std::num::Zero;
 use std::sync::atomics::Relaxed;
@@ -65,7 +66,7 @@ use style::computed_values::{clear, position, text_align};
 ///
 /// Note that virtual methods have a cost; we should not overuse them in Servo. Consider adding
 /// methods to `ImmutableFlowUtils` or `MutableFlowUtils` before adding more methods here.
-pub trait Flow {
+pub trait Flow: fmt::Show + ToStr {
     // RTTI
     //
     // TODO(pcwalton): Use Rust's RTTI, once that works.
@@ -267,11 +268,6 @@ pub trait Flow {
             LayerId(pointer, fragment_id)
         }
     }
-
-    /// Returns a debugging string describing this flow.
-    fn debug_str(&self) -> ~str {
-        "???".to_owned()
-    }
 }
 
 // Base access
@@ -915,7 +911,7 @@ impl<'a> ImmutableFlowUtils for &'a Flow {
         for _ in range(0, level) {
             indent.push_str("| ")
         }
-        debug!("{}+ {}", indent, self.debug_str());
+        debug!("{}+ {}", indent, self.to_str());
         for kid in imm_child_iter(self) {
             kid.dump_with_level(level + 1)
         }
diff --git a/src/components/main/layout/inline.rs b/src/components/main/layout/inline.rs
index ec79256f1e5..17a52899c37 100644
--- a/src/components/main/layout/inline.rs
+++ b/src/components/main/layout/inline.rs
@@ -22,6 +22,7 @@ use servo_util::geometry::Au;
 use servo_util::geometry;
 use servo_util::range::Range;
 use std::iter::Enumerate;
+use std::fmt;
 use std::mem;
 use std::slice::{Items, MutItems};
 use std::u16;
@@ -235,8 +236,8 @@ impl LineboxScanner {
         // try_append_to_line.
         match first_box.split_to_width(line_bounds.size.width, line_is_empty) {
             CannotSplit => {
-                error!("LineboxScanner: Tried to split unsplittable render box! {:s}",
-                        first_box.debug_str());
+                error!("LineboxScanner: Tried to split unsplittable render box! {}",
+                        first_box);
                 return (line_bounds, first_box_size.width);
             }
             SplitDidFit(left, right) => {
@@ -356,11 +357,11 @@ impl LineboxScanner {
         }
 
         debug!("LineboxScanner: Trying to append box to line {:u} (box size: {}, green zone: \
-                {}): {:s}",
+                {}): {}",
                self.lines.len(),
                in_box.border_box.size,
                self.pending_line.green_zone,
-               in_box.debug_str());
+               in_box);
 
         let green_zone = self.pending_line.green_zone;
 
@@ -400,8 +401,8 @@ impl LineboxScanner {
         let split = in_box.split_to_width(available_width, line_is_empty);
         let (left, right) = match (split, line_is_empty) {
             (CannotSplit, _) => {
-                debug!("LineboxScanner: Tried to split unsplittable render box! {:s}",
-                        in_box.debug_str());
+                debug!("LineboxScanner: Tried to split unsplittable render box! {}",
+                        in_box);
                 self.work_list.push_front(in_box);
                 return false
             }
@@ -756,7 +757,7 @@ impl Flow for InlineFlow {
 
         let mut intrinsic_widths = IntrinsicWidths::new();
         for (fragment, context) in self.boxes.mut_iter() {
-            debug!("Flow: measuring {:s}", fragment.debug_str());
+            debug!("Flow: measuring {}", *fragment);
 
             let box_intrinsic_widths = fragment.intrinsic_widths(Some(context));
             intrinsic_widths.minimum_width = geometry::max(intrinsic_widths.minimum_width,
@@ -954,16 +955,19 @@ impl Flow for InlineFlow {
         self.base.floats = scanner.floats();
         self.base.floats.translate(Point2D(Au::new(0), -self.base.position.size.height));
     }
+}
 
-    fn debug_str(&self) -> ~str {
-        let mut string = "InlineFlow: ".to_str();
+impl fmt::Show for InlineFlow {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        try!(write!(f.buf, "InlineFlow"));
         for (i, (fragment, _)) in self.boxes.iter().enumerate() {
-            if i != 0 {
-                string.push_str(", ")
+            if i == 0 {
+                try!(write!(f.buf, ": {}", fragment))
+            } else {
+                try!(write!(f.buf, ", {}", fragment))
             }
-            string.push_str(fragment.debug_str())
         }
-        string
+        Ok(())
     }
 }
 
diff --git a/src/components/main/layout/table.rs b/src/components/main/layout/table.rs
index feed2585d4a..d3b67699073 100644
--- a/src/components/main/layout/table.rs
+++ b/src/components/main/layout/table.rs
@@ -16,6 +16,7 @@ use layout::wrapper::ThreadSafeLayoutNode;
 
 use servo_util::geometry::Au;
 use servo_util::geometry;
+use std::fmt;
 use style::computed_values::table_layout;
 
 /// A table flow corresponded to the table's internal table box under a table wrapper flow.
@@ -287,10 +288,12 @@ impl Flow for TableFlow {
     fn compute_absolute_position(&mut self) {
         self.block_flow.compute_absolute_position()
     }
+}
 
-    fn debug_str(&self) -> ~str {
-        let txt = "TableFlow: ".to_owned();
-        txt.append(self.block_flow.box_.debug_str())
+impl fmt::Show for TableFlow {
+    /// Outputs a debugging string describing this table flow.
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "TableFlow: {}", self.block_flow)
     }
 }
 
diff --git a/src/components/main/layout/table_caption.rs b/src/components/main/layout/table_caption.rs
index 8e0cbb86176..d53bf0e52b1 100644
--- a/src/components/main/layout/table_caption.rs
+++ b/src/components/main/layout/table_caption.rs
@@ -10,6 +10,8 @@ use layout::context::LayoutContext;
 use layout::flow::{TableCaptionFlowClass, FlowClass, Flow};
 use layout::wrapper::ThreadSafeLayoutNode;
 
+use std::fmt;
+
 /// A table formatting context.
 pub struct TableCaptionFlow {
     pub block_flow: BlockFlow,
@@ -60,9 +62,10 @@ impl Flow for TableCaptionFlow {
     fn compute_absolute_position(&mut self) {
         self.block_flow.compute_absolute_position()
     }
+}
 
-    fn debug_str(&self) -> ~str {
-        let txt = "TableCaptionFlow: ".to_owned();
-        txt.append(self.block_flow.box_.debug_str())
+impl fmt::Show for TableCaptionFlow {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "TableCaptionFlow: {}", self.block_flow)
     }
 }
diff --git a/src/components/main/layout/table_cell.rs b/src/components/main/layout/table_cell.rs
index 389ed6143f7..da1dd6ea6eb 100644
--- a/src/components/main/layout/table_cell.rs
+++ b/src/components/main/layout/table_cell.rs
@@ -13,6 +13,7 @@ use layout::table::InternalTable;
 use layout::wrapper::ThreadSafeLayoutNode;
 
 use servo_util::geometry::Au;
+use std::fmt;
 
 /// A table formatting context.
 pub struct TableCellFlow {
@@ -109,10 +110,10 @@ impl Flow for TableCellFlow {
     fn compute_absolute_position(&mut self) {
         self.block_flow.compute_absolute_position()
     }
-
-    fn debug_str(&self) -> ~str {
-        let txt = "TableCellFlow: ".to_owned();
-        txt.append(self.block_flow.box_.debug_str())
-    }
 }
 
+impl fmt::Show for TableCellFlow {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "TableCellFlow: {}", self.block_flow)
+    }
+}
diff --git a/src/components/main/layout/table_colgroup.rs b/src/components/main/layout/table_colgroup.rs
index 5ac1ab81376..004d18d751f 100644
--- a/src/components/main/layout/table_colgroup.rs
+++ b/src/components/main/layout/table_colgroup.rs
@@ -9,7 +9,9 @@ use layout::context::LayoutContext;
 use layout::flow::{BaseFlow, TableColGroupFlowClass, FlowClass, Flow};
 use layout::model::{MaybeAuto};
 use layout::wrapper::ThreadSafeLayoutNode;
+
 use servo_util::geometry::Au;
+use std::fmt;
 
 /// A table formatting context.
 pub struct TableColGroupFlow {
@@ -72,12 +74,13 @@ impl Flow for TableColGroupFlow {
     /// Table column do not have height.
     fn assign_height(&mut self, _ctx: &mut LayoutContext) {
     }
+}
 
-    fn debug_str(&self) -> ~str {
-        let txt = "TableColGroupFlow: ".to_owned();
-        txt.append(match self.box_ {
-            Some(ref rb) => rb.debug_str(),
-            None => "".to_owned(),
-        })
+impl fmt::Show for TableColGroupFlow {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self.box_ {
+            Some(ref rb) => write!(f.buf, "TableColGroupFlow: {}", rb),
+            None => write!(f.buf, "TableColGroupFlow"),
+        }
     }
 }
diff --git a/src/components/main/layout/table_row.rs b/src/components/main/layout/table_row.rs
index c49a78a8579..036f53e85cd 100644
--- a/src/components/main/layout/table_row.rs
+++ b/src/components/main/layout/table_row.rs
@@ -17,6 +17,7 @@ use layout::wrapper::ThreadSafeLayoutNode;
 
 use servo_util::geometry::Au;
 use servo_util::geometry;
+use std::fmt;
 
 /// A table formatting context.
 pub struct TableRowFlow {
@@ -213,10 +214,10 @@ impl Flow for TableRowFlow {
     fn compute_absolute_position(&mut self) {
         self.block_flow.compute_absolute_position()
     }
-
-    fn debug_str(&self) -> ~str {
-        let txt = "TableRowFlow: ".to_owned();
-        txt.append(self.block_flow.box_.debug_str())
-    }
 }
 
+impl fmt::Show for TableRowFlow {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "TableRowFlow: {}", self.block_flow.box_)
+    }
+}
diff --git a/src/components/main/layout/table_rowgroup.rs b/src/components/main/layout/table_rowgroup.rs
index eb779fd96ca..794a7d12493 100644
--- a/src/components/main/layout/table_rowgroup.rs
+++ b/src/components/main/layout/table_rowgroup.rs
@@ -16,6 +16,7 @@ use layout::wrapper::ThreadSafeLayoutNode;
 
 use servo_util::geometry::Au;
 use servo_util::geometry;
+use std::fmt;
 
 /// A table formatting context.
 pub struct TableRowGroupFlow {
@@ -195,10 +196,10 @@ impl Flow for TableRowGroupFlow {
     fn compute_absolute_position(&mut self) {
         self.block_flow.compute_absolute_position()
     }
-
-    fn debug_str(&self) -> ~str {
-        let txt = "TableRowGroupFlow: ".to_owned();
-        txt.append(self.block_flow.box_.debug_str())
-    }
 }
 
+impl fmt::Show for TableRowGroupFlow {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f.buf, "TableRowGroupFlow: {}", self.block_flow.box_)
+    }
+}
diff --git a/src/components/main/layout/table_wrapper.rs b/src/components/main/layout/table_wrapper.rs
index ad1a66eace0..69ef004ede6 100644
--- a/src/components/main/layout/table_wrapper.rs
+++ b/src/components/main/layout/table_wrapper.rs
@@ -16,6 +16,7 @@ use layout::wrapper::ThreadSafeLayoutNode;
 
 use servo_util::geometry::Au;
 use servo_util::geometry;
+use std::fmt;
 use style::computed_values::table_layout;
 
 pub enum TableLayout {
@@ -188,14 +189,15 @@ impl Flow for TableWrapperFlow {
     fn compute_absolute_position(&mut self) {
         self.block_flow.compute_absolute_position()
     }
+}
 
-    fn debug_str(&self) -> ~str {
-        let txt = if self.is_float() {
-            "TableWrapperFlow(Float): ".to_owned()
+impl fmt::Show for TableWrapperFlow {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if self.is_float() {
+            write!(f.buf, "TableWrapperFlow(Float): {}", self.block_flow.box_)
         } else {
-            "TableWrapperFlow: ".to_owned()
-        };
-        txt.append(self.block_flow.box_.debug_str())
+            write!(f.buf, "TableWrapperFlow: {}", self.block_flow.box_)
+        }
     }
 }
 
diff --git a/src/components/main/layout/text.rs b/src/components/main/layout/text.rs
index 3757bef9d80..c70aa8c0cb1 100644
--- a/src/components/main/layout/text.rs
+++ b/src/components/main/layout/text.rs
@@ -237,8 +237,7 @@ impl TextRunScanner {
                     let range = new_ranges.get(logical_offset);
                     if range.length() == 0 {
                         debug!("Elided an `UnscannedTextbox` because it was zero-length after \
-                                compression; {:s}",
-                               in_boxes[i].debug_str());
+                                compression; {}", in_boxes[i]);
                         continue
                     }