diff --git a/package.json b/package.json
index e7e4340..3282ef0 100644
--- a/package.json
+++ b/package.json
@@ -5,7 +5,7 @@
   "type": "module",
   "description": "Browser extension for subscribing to standard.site publications on the AT Protocol",
   "scripts": {
-    "build": "vite build && vite build --config vite.content.config.ts",
+    "build": "vite build",
     "check": "tsc --noEmit"
   },
   "dependencies": {
diff --git a/vite.config.ts b/vite.config.ts
index f4e48c6..0e6566d 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -1,23 +1,46 @@
 import { defineConfig } from 'vite'
 import { resolve } from 'node:path'
 
-// Builds the popup page and the background service worker. The content script
-// needs its own IIFE build; see vite.content.config.ts. `npm run build` runs both.
+// One build, two environments (Vite 6 builder API — `vite build` builds both
+// in order):
+//
+// - `client`: the popup/auth pages and the background service worker, as ES
+//   modules. Empties dist/ and copies public/ (manifest, icons).
+// - `content`: the content script as a single IIFE file, because MV3 content
+//   scripts cannot be ES modules. Builds second, into the same dist/.
+//
+// scripts/dev.mjs runs the same two environments in watch mode.
 export default defineConfig({
-  build: {
-    outDir: 'dist',
-    emptyOutDir: true,
-    modulePreload: false,
-    rollupOptions: {
-      input: {
-        popup: resolve(__dirname, 'popup.html'),
-        auth: resolve(__dirname, 'auth.html'),
-        background: resolve(__dirname, 'src/background.ts'),
+  builder: {},
+  environments: {
+    client: {
+      build: {
+        modulePreload: false,
+        rollupOptions: {
+          input: {
+            popup: resolve(__dirname, 'popup.html'),
+            auth: resolve(__dirname, 'auth.html'),
+            background: resolve(__dirname, 'src/background.ts'),
+          },
+          output: {
+            entryFileNames: '[name].js',
+            chunkFileNames: 'chunks/[name]-[hash].js',
+            assetFileNames: 'assets/[name][extname]',
+          },
+        },
       },
-      output: {
-        entryFileNames: '[name].js',
-        chunkFileNames: 'chunks/[name]-[hash].js',
-        assetFileNames: 'assets/[name][extname]',
+    },
+    content: {
+      consumer: 'client',
+      build: {
+        emptyOutDir: false, // shares dist/ with the client environment
+        copyPublicDir: false,
+        lib: {
+          entry: resolve(__dirname, 'src/content.ts'),
+          name: 'substandardContent',
+          formats: ['iife'],
+          fileName: () => 'content.js',
+        },
       },
     },
   },
diff --git a/vite.content.config.ts b/vite.content.config.ts
deleted file mode 100644
index c87e220..0000000
--- a/vite.content.config.ts
+++ /dev/null
@@ -1,17 +0,0 @@
-import { defineConfig } from 'vite'
-import { resolve } from 'node:path'
-
-// Content scripts cannot be ES modules, so build content.ts separately as an IIFE.
-export default defineConfig({
-  build: {
-    outDir: 'dist',
-    emptyOutDir: false,
-    copyPublicDir: false,
-    lib: {
-      entry: resolve(__dirname, 'src/content.ts'),
-      name: 'substandardContent',
-      formats: ['iife'],
-      fileName: () => 'content.js',
-    },
-  },
-})