diff --git a/README.md b/README.md
index 881b69c..982a2f7 100644
--- a/README.md
+++ b/README.md
@@ -112,4 +112,4 @@ Każdy problem zostanie sprawdzony i przeniesiony na wewnętrzną listę problem
 
 ---
 
-# Test pre-commit hook
+# Test pre-commit hook - without Docker check
diff --git a/esbuild.config.js b/esbuild.config.js
index 47416f9..13b6e4f 100644
--- a/esbuild.config.js
+++ b/esbuild.config.js
@@ -1,5 +1,7 @@
 import esbuild from 'esbuild';
 import scss from 'esbuild-plugin-sass';
+import fs from 'fs';
+import path from 'path';
 
 const watch = process.argv.includes('--watch') && {
     onRebuild(error) {
@@ -73,5 +75,34 @@ esbuild
         external: ['react', 'react-dom', 'survey-react'],
         watch,
     })
-    .then(() => console.log('Add-on was built'))
+    .then(() => {
+        console.log('Add-on was built');
+
+        // Modify manifest.json to include test content script when ENABLE_TESTS=true
+        if (ENABLE_TESTS) {
+            const manifestPath = path.join(process.cwd(), 'manifest.json');
+            const manifest = JSON.parse(fs.readFileSync(manifestPath, 'utf-8'));
+
+            // Add content_scripts for testing
+            if (!manifest.content_scripts) {
+                manifest.content_scripts = [];
+            }
+
+            // Check if test script is already added
+            const hasTestScript = manifest.content_scripts.some(
+                cs => cs.js && cs.js.includes('lib/tests/test-content-script.js')
+            );
+
+            if (!hasTestScript) {
+                manifest.content_scripts.push({
+                    matches: ['<all_urls>'],
+                    js: ['lib/tests/test-content-script.js'],
+                    run_at: 'document_start'
+                });
+
+                fs.writeFileSync(manifestPath, JSON.stringify(manifest, null, 4));
+                console.log('Added test content script to manifest.json');
+            }
+        }
+    })
     .catch(() => process.exit(1));
diff --git a/tests/test-lib.js b/tests/test-lib.js
index 5c96350..00f782f 100644
--- a/tests/test-lib.js
+++ b/tests/test-lib.js
@@ -2,24 +2,21 @@
 // This JavaScript code runs in the browser context via Marionette
 
 /**
- * Inject test content script into the page
- * @returns {Promise<boolean>} - True if injection successful
+ * Check if test content script is loaded
+ * The content script is automatically injected by manifest.json when ENABLE_TESTS=true
+ * @returns {Promise<boolean>} - True if content script is loaded
  */
-async function injectTestContentScript() {
-    // Read the content script file
-    const response = await fetch(browser.runtime.getURL('lib/tests/test-content-script.js'));
-    const scriptCode = await response.text();
-
-    // Inject it into the page
-    const script = document.createElement('script');
-    script.textContent = scriptCode;
-    document.documentElement.appendChild(script);
-    script.remove();
-
-    // Wait a bit for script to initialize
-    await new Promise(resolve => setTimeout(resolve, 100));
-
-    return document.body.getAttribute('data-rentgen-injected') === 'true';
+async function waitForTestContentScript() {
+    // Wait for content script to set the marker
+    let attempts = 0;
+    while (attempts < 50) {
+        if (document.body && document.body.getAttribute('data-rentgen-injected') === 'true') {
+            return true;
+        }
+        await new Promise(resolve => setTimeout(resolve, 100));
+        attempts++;
+    }
+    return false;
 }
 
 /**
@@ -28,9 +25,9 @@ async function injectTestContentScript() {
  * @returns {Promise<number|null>} - Badge count (number of third-party domains) or null on failure
  */
 async function testBadgeCount() {
-    // Inject content script first
-    const injected = await injectTestContentScript();
-    if (!injected) {
+    // Wait for content script to be loaded
+    const loaded = await waitForTestContentScript();
+    if (!loaded) {
         return -1;  // Content script not loaded
     }