CSS hack, browser Selection

Less than IE6
* HTML {}

Less than IE 7
*: First-Child + HTML {} * HTML {}

Only for IE 7
*: First-Child + HTML {}

Only for IE 7 and modern browsers
HTML> body {}

Only for modern browsers (not IE 7)
HTML>/**/body {}

Latest versions of opera 9 or earlier
HTML: First-child {}

Safari
HTML [xmlns * = ""] body: Last-child {}

Firefox 3
. Classname, X:-moz-any-link, X: Default {}
# ID, X:-moz-any-link, X: Default {}

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Difference between IE6 and FF:
Background: orange; * Background: blue;

Difference between IE6 and IE7:
Background: Green! Important; Background: blue;
Difference between IE7 and FF:
Background: orange; * Background: green;

Difference ff, IE7, IE6:
Background: orange; * Background: Green! Important; * Background: blue;

Difference ff 3
Add ", X:-moz-any-link, X: Default" before "{", and only FF 3 can recognize it.

Note:
Ie can recognize *; standard browsers (such as ff) cannot recognize *;
IE6 can recognize *, but cannot recognize it! Important,
IE7 can recognize * and can also recognize! Important;
FF cannot recognize *, but can recognize it! Important;