I am viewing a CSS edited blog with Firefox 3.6.16 however as I don't know what to expect and what ought to be displaying I can't be very helpful.
Have you tried logging out and clearing your browser cache and cookies and then logging in again? If that does not work then you can try viewing the blog in another browser. Instructions here > http://en.support.wordpress.com/browser-issues/
Have you changed your theme? CSS is theme specific. If you have custom CSS and later change themes, you need to delete whatever CSS you have in the Editor, otherwise, you’ll get undesired results.
To ‘reset’ a theme, you need to delete the CSS in the Editor, make sure the “add to existing CSS” radio button is checked, then save. Things should go back to normal.
When you alter a theme’s stylesheet, you only need to put in the Editor the modification/additions to the CSS, not the entire thing. Read this for more info:
If the issue still persists you will have to contact Staff > http://en.support.wordpress.com/contact/