In CSS 2, IE/Win doesn't support the following selectors:

• adjacent sibling selectors (E1 + E2);
• attribute selectors (E[foo], E[foo="warning"], E[foo~="warning"], and E[lang|="en"]);
• child selectors (E > F).

Netscape 4.x doesn’t support:

• adjacent sibling selectors;
• attribute selectors;
• child selectors;
• universal selectors (*);
• most (if not all) ID selectors with an element prefix (E#myid).

Internet Explorer 5.x on the Macintosh doesn’t support:

• attribute selectors.

Mozilla (and similar browsers), Opera, and Safari should support all of CSS 2’s selectors. For CSS 3 selectors, visit the Guide to CSS3 Selector Support.