It is best to turn off your WYSIWYG/content editor as it strips out HTML which you need for that function. Do the following to disable:
1. Login into the Joomla Administrator
2. Go to Site -> Global Configuration
3. Locate the field Default WYSIWYG Editor:
4. From the dropdown, select No WYSIWYG editor
5. Save
Alternatively, you can disable it for your account only:
1. Login to the Joomla Administrator
2. Go to Site -> User Manager -> Your Account
3. Select No WYSIWYG editor from the dropdown