CSS editing is always a multi-check job because of getting different results for every browser. This time-consuming design process gets easier with CSSVista.

CSSVista is a free Windows application for web developers which lets you edit your CSS code live in both Internet Explorer and Firefox simultaneously.

With small modifications, it may be easier to work with the default html/css editor that you are using but with large updates of CSS files or creating a new one, you might want to take a look at CSSVista.