diff --git a/pkgs/by-name/om/omnom/package.nix b/pkgs/by-name/om/omnom/package.nix
index 8074a8ce4f94..837c72984180 100644
--- a/pkgs/by-name/om/omnom/package.nix
+++ b/pkgs/by-name/om/omnom/package.nix
@@ -34,55 +34,54 @@ buildGoModule (finalAttrs: {
     "-w"
   ];
 
-  postBuild =
-    let
-      omnom-addons = buildNpmPackage {
-        pname = "omnom-addons";
-        inherit (finalAttrs) version src;
-
-        npmDepsHash = "sha256-sUn5IvcHWJ/yaqeGz9SGvGx9HHAlrcnS0lJxIxUVS6M=";
-        sourceRoot = "${finalAttrs.src.name}/ext";
-        npmPackFlags = [ "--ignore-scripts" ];
-
-        nativeBuildInputs = [ zip ];
-
-        # Fix path for the `static` directory
-        postConfigure = ''
-          substituteInPlace webpack.config.js \
-          --replace-fail '"..", ".."' '".."'
-        '';
-
-        postBuild = ''
-          mkdir -p $out
-
-          zip -r "$out/omnom_ext_src.zip" README.md src utils package* webpack.config.js
-
-          pushd build
-            zip "$out/omnom_ext_chrome.zip" ./* icons/* -x manifest_ff.json
-            zip "$out/omnom_ext_firefox.zip" ./* icons/* -x manifest_ff.json
-          popd
-        '';
-
-        postCheck = ''
-          npm run build-test
-        '';
-      };
-    in
-    ''
-      mkdir -p $out/share/addons
-
-      # Copy Firefox and Chrome addons
-      cp -r ${omnom-addons}/*.zip $out/share/addons
-    '';
-
   postInstall = ''
+    mkdir -p $out/share/addons
+
+    # Copy Firefox and Chrome addons
+    cp -r ${finalAttrs.passthru.omnom-addons}/*.zip $out/share/addons
+
     mkdir -p $out/share/examples
 
     cp -r static templates $out/share
     cp config.yml_sample $out/share/examples/config.yml
   '';
 
-  passthru.tests = nixosTests.omnom;
+  passthru = {
+    omnom-addons = buildNpmPackage (finalAttrs': {
+      pname = "omnom-addons";
+      inherit (finalAttrs) version src;
+
+      npmDepsHash = "sha256-sUn5IvcHWJ/yaqeGz9SGvGx9HHAlrcnS0lJxIxUVS6M=";
+      sourceRoot = "${finalAttrs'.src.name}/ext";
+      npmPackFlags = [ "--ignore-scripts" ];
+
+      nativeBuildInputs = [ zip ];
+
+      # Fix path for the `static` directory
+      postConfigure = ''
+        substituteInPlace webpack.config.js \
+        --replace-fail '"..", ".."' '".."'
+      '';
+
+      postBuild = ''
+        mkdir -p $out
+
+        zip -r "$out/omnom_ext_src.zip" README.md src utils package* webpack.config.js
+
+        pushd build
+          zip "$out/omnom_ext_chrome.zip" ./* icons/* -x manifest_ff.json
+          cp manifest_ff.json manifest.json
+          zip "$out/omnom_ext_firefox.zip" ./* icons/* -x manifest_ff.json
+        popd
+      '';
+
+      postCheck = ''
+        npm run build-test
+      '';
+    });
+
+    tests = nixosTests.omnom;
+  };
 
   meta = {
     description = "Webpage bookmarking and snapshotting service";