diff --git a/.semaphore/semaphore.yml b/.semaphore/semaphore.yml
index 1fe5d5102e5..65a1bfb4104 100644
--- a/.semaphore/semaphore.yml
+++ b/.semaphore/semaphore.yml
@@ -43,6 +43,9 @@ blocks:
         - name: enterprise mock - standard test group
           commands:
             - npm run-script test_ci_chrome_enterprise
+        - name: thunderbird test
+          commands:
+            - npm run-script test_thunderbird
       epilogue:
         always:
           commands:
diff --git a/conf/tsconfig.test.json b/conf/tsconfig.test.json
index 0aa1ba1d290..20529dc4da9 100644
--- a/conf/tsconfig.test.json
+++ b/conf/tsconfig.test.json
@@ -19,6 +19,7 @@
     "../extension/types/node-forge.d.ts",
     "../test/source/test.ts",
     "../test/source/patterns.ts",
+    "../test/source/thunderbird-manifest-v2-test.ts",
     "../test/source/async-stack.ts",
     "../test/source/buf.ts"
   ]
diff --git a/package.json b/package.json
index 2203f916744..c854aee9e60 100644
--- a/package.json
+++ b/package.json
@@ -78,6 +78,7 @@
     "test_eslint": "export NODE_OPTIONS=\"--max-old-space-size=4096\"; eslint .",
     "test_eslint_ci": "npm run test_eslint -- --format @microsoft/eslint-formatter-sarif --output-file eslint-results.sarif",
     "test_patterns": "node build/test/test/source/patterns.js",
+    "test_thunderbird": "npm run pretest && node build/test/test/source/thunderbird-manifest-v2-test.js",
     "test_async_stack": "node build/test/test/source/async-stack.js",
     "test_buf": "npx ava --timeout=3m --verbose --concurrency=10 build/test/test/source/buf.js",
     "test_ci_chrome_consumer_live_gmail": "npx ava --timeout=45m --verbose --tap --concurrency=1 build/test/test/source/test.js -- CONSUMER-LIVE-GMAIL STANDARD-GROUP | npx tap-xunit > report.xml",
diff --git a/test/source/thunderbird-manifest-v2-test.ts b/test/source/thunderbird-manifest-v2-test.ts
new file mode 100644
index 00000000000..f17b3417bbc
--- /dev/null
+++ b/test/source/thunderbird-manifest-v2-test.ts
@@ -0,0 +1,26 @@
+/* ©️ 2016 - present FlowCrypt a.s. Limitations apply. Contact human@flowcrypt.com */
+import * as fs from 'fs';
+
+/* This test looks for any unexpected change for Thunderbird port of FlowCrypt ensuring its using Manifest v2 */
+
+const manifestPath = 'build/thunderbird-consumer/manifest.json';
+const manifestContent = fs.readFileSync(manifestPath, 'utf8');
+const manifest = JSON.parse(manifestContent);
+
+const testManifestV2Format = () => {
+  try {
+    if (manifest.manifest_version !== 2) {
+      throw new Error('Manifest version is not 2');
+    }
+    if (!Array.isArray(manifest.web_accessible_resources)) {
+      throw new Error('web_accessible_resources should be an array');
+    }
+    if (typeof manifest.content_security_policy !== 'string') {
+      throw new Error('content_security_policy should be a string');
+    }
+  } catch (error) {
+    console.error('Manifest V2 format test failed:', error.message);
+  }
+};
+
+testManifestV2Format();