[test] Added new testcase for validating firefox browser

Author: ravishankar

s_tool/utils/__init__.py

@@ -0,0 +1,7 @@
+from s_tool.driver import SeleniumDriver
+
+
+def test_firefox_driver():
+    """Test firefox driver with headless"""
+    with SeleniumDriver("firefox", headless=True) as obj:
+        assert "firefox" in obj.browser_list