There are browser extensions which can inject html into the editor and can cause problems.  If we detect an unsupported extension while using the HTML editor we will disable the editor and you will not be able to edit or save.

You must disable the extension before you can continue to use the editor.  If you have already disabled the extension and are still not able to edit, please revert to an older version using the snapshot manager.  If this still has not helped please contact support.

Below, is more information on the error and a list of unsupported extensions.