Entering raw HTML in editors
From Joomla! Documentation
If you want to enter raw HTML in a Joomla! editor field, you may encounter problems such as tags and attributes disappearing after you save the item you are editing. This is usually caused by a filtering mechanism; either your editor's or Joomla!'s.
On the Administrator panel, take the following steps to disable filtering:
- Disable your editor. Since each editor has its own filtering mechanism and it is not always possible to turn it off, disabling your editor is the easiest way of eliminating it as a possible source of the problem. Open My Profile from the Site menu, set Editor under Basic Settings to Editor - None and click Save & Close.
- Disable Joomla's filtering. Open the Global Configuration from the Site menu and go to the Text Filters tab. Set the Filter Type to No Filtering for the user group that you are in - Administrator, Super Users, or both (this is site-dependent). Caution: Do not use the No Filtering setting for user groups that are not fully trusted – that would introduce a sizeable security risk.
You should be able to enter raw HTML in any editor field now. You may try to re-enable your editor to see whether it influences the process. If the editor does mangle the HTML you are trying to enter, consult its documentation to see if there is a way to disable its filtering.