We have two ways that could be solve the CSS compatibility problem.

  1. !important

    IE7&FF support !important,so we can use!important to focus on IE6.(Must write above.)

    #wrapper
    {
    width: 100px!important; /* IE7+FF */
    width: 80px; /* IE6 */
    }

  2. IE6/IE7 vs FireFox

    *html is IE-only lable, FireFox is not supprt. *+html is IE7 only.

    #wrapper
    {
    #wrapper { width: 120px; } /* FireFox */
    *html #wrapper { width: 80px;} /* ie6 fixed */
    *+html #wrapper { width: 60px;} /* ie7 fixed, must ordered like this */
    }

    Notice: this method is loose definition.
    <!DOCTYPE HTML PUBLIC 『-//W3C//DTD HTML 4.01 Transitional//EN』　』http://www.w3.org/TR/html4/loose.dtd『>

There are three Reference for comparing css of web bowsers:

Browser Bug Reference

CSS Compatibility Table

DOM Compatibility Table