CKEDITOR may load its own css files to customize the view of the contents during their editing (only during editing, though…).
Here is the process in FF to make sure that any changes done to the CSS is taken notice of, right away.
1) Have a separated tab where the URL of the css is called.
2) after any changes to the CSS, give a F5 in the above mentioned tab.
3) give a F5 in the page where CKEDITOR is running.