diff --git a/product/ERP5Type/tests/ERP5TypeFunctionalTestCase.py b/product/ERP5Type/tests/ERP5TypeFunctionalTestCase.py
index 352542a52c18808483941125a7ce17b153f6e225..75f2c311806ed8fa58423f5551c0f1ff65b013d0 100644
--- a/product/ERP5Type/tests/ERP5TypeFunctionalTestCase.py
+++ b/product/ERP5Type/tests/ERP5TypeFunctionalTestCase.py
@@ -241,6 +241,11 @@ user_pref("browser.download.folderList", 2);
 user_pref("browser.download.manager.showWhenStarting", false);
 user_pref("browser.download.dir", "%s");
 user_pref("browser.helperApps.neverAsk.saveToDisk", "application/pdf");
+// Otherwise clear previously defined PDF-related extensions
+// => browser/extensions/pdfjs/content/PdfJs.jsm:_migrate()
+user_pref("pdfjs.disabled", true);
+// Not really necessary (just FTR)
+user_pref("pdfjs.migrationVersion", 42);
 """ % (self.host, self.port,
        os.path.join(getConfiguration().instancehome, 'var'))