diff --git a/gfx/thebes/gfxHarfBuzzShaper.cpp b/gfx/thebes/gfxHarfBuzzShaper.cpp
index 18bc08a6bf..46e0675aa2 100644
--- a/gfx/thebes/gfxHarfBuzzShaper.cpp
+++ b/gfx/thebes/gfxHarfBuzzShaper.cpp
@@ -17,6 +17,9 @@
 
 #include "harfbuzz/hb.h"
 #include "harfbuzz/hb-ot.h"
+#include <cstdlib>
+#include <chrono>
+#include "MaskConfig.hpp"
 
 #include <algorithm>
 
@@ -1557,6 +1560,36 @@ bool gfxHarfBuzzShaper::ShapeText(DrawTarget* aDrawTarget,
 
   hb_shape(mHBFont, mBuffer, features.Elements(), features.Length());
 
+  static uint32_t seed;
+  if (auto value = MaskConfig::GetUint32("fonts:spacing_seed"))
+    seed = value.value();
+  else
+    seed = static_cast<uint32_t>(
+        std::chrono::high_resolution_clock::now().time_since_epoch().count());
+
+  // Generate a random float [0, 0.1] to offset the letter spacing
+  seed = (seed * 1103515245 + 12345) & 0x7fffffff;
+  float randomFloat = (static_cast<float>(seed) / 0x7fffffff) * 0.1f;
+  hb_position_t spacing = FloatToFixed(randomFloat);
+
+  uint32_t glyphCount;
+  hb_glyph_position_t* glyphPositions =
+      hb_buffer_get_glyph_positions(mBuffer, &glyphCount);
+
+  hb_position_t cumulativeOffset = 0;
+
+  // Apply custom letter spacing
+  for (uint32_t i = 0; i < glyphCount; ++i) {
+    if (aVertical) {
+      glyphPositions[i].y_advance -= spacing;
+      glyphPositions[i].y_offset -= cumulativeOffset;
+    } else {
+      glyphPositions[i].x_advance += spacing;
+      glyphPositions[i].x_offset += cumulativeOffset;
+    }
+    cumulativeOffset += spacing;
+  }
+
   if (isRightToLeft) {
     hb_buffer_reverse(mBuffer);
   }