diff --git a/home/librewolf.nix b/home/librewolf.nix
index fbb088ca..ee4f477b 100644
--- a/home/librewolf.nix
+++ b/home/librewolf.nix
@@ -24,6 +24,7 @@ in
         yomitan
         redlib
         new-tab-identity
+        showdex
       ];
 
       search = {
diff --git a/packages/showdex.nix b/packages/showdex.nix
new file mode 100644
index 00000000..40367b7c
--- /dev/null
+++ b/packages/showdex.nix
@@ -0,0 +1,33 @@
+{
+  lib,
+  stdenvNoCC,
+  fetchurl,
+}:
+
+stdenvNoCC.mkDerivation (finalAttrs: {
+  pname = "showdex";
+  version = "1.2.4";
+
+  src = fetchurl {
+    url = "https://addons.mozilla.org/firefox/downloads/file/4329311/showdex-${finalAttrs.version}.xpi";
+    hash = "sha256-V2TbyhrB1mrkF7PdJrPdvN+umJXbEcbSKA2jfVPFvV8=";
+  };
+
+  dontUnpack = true;
+
+  installPhase = ''
+    runHook preInstall
+
+    install -Dm644 "$src" "$out/share/mozilla/extensions/{ec8030f7-c20a-464f-9b0e-13a3a9e97384}/showdex@tize.io.xpi"
+
+    runHook postInstall
+  '';
+
+  meta = {
+    homepage = "https://github.com/doshidak/showdex";
+    description = "Pokémon Showdown extension that harnesses the power of parabolic calculus to strategically extract your opponents' Elo";
+    license = lib.licenses.agpl3Only;
+    maintainers = with lib.maintainers; [ donovanglover ];
+    platforms = lib.platforms.all;
+  };
+})