diff --git a/package.json b/package.json
index 3053651d..73886a86 100644
--- a/package.json
+++ b/package.json
@@ -28,11 +28,11 @@
   },
   "scripts": {
     "lint": "eslint \"**/*.js\" --cache",
-    "test": "npm run lint",
+    "test": "node tools/test.js && npm run lint",
     "update-locales": "tx pull --all && node tools/fix-transifex.js",
     "update-transifex": "tx push -s",
     "build-vendor": "node tools/build-vendor",
-    "zip": "node tools/zip.js",
+    "zip": "npm test && node tools/zip.js",
     "start": "web-ext run",
     "start-chrome": "web-ext run -t chromium",
     "preversion": "npm test",
diff --git a/tools/test.js b/tools/test.js
new file mode 100644
index 00000000..0134ac58
--- /dev/null
+++ b/tools/test.js
@@ -0,0 +1,16 @@
+'use strict';
+
+const fs = require('fs');
+
+testGlobalCss();
+
+function testGlobalCss() {
+  const css = fs.readFileSync('global.css', {encoding: 'utf8'});
+  const ERR = 'global.css: the first rule must be the transition suppressor';
+  const RX_SUPPRESSOR = /^[^{}]+{\s*transition:\s*none\s*!\s*important/i;
+  const RX_COMMENT = /\/\*([^*]|\*(?!\/))*(\*\/|$)/g;
+  if (!RX_SUPPRESSOR.test(css.replace(RX_COMMENT, ''))) {
+    console.error(ERR);
+    process.exit(1);
+  }
+}