Differentiate between CSShack _ experiences in IE6, IE7, and firefox

Web page layout often requires a part-time multi-browser, so the following csshack can be used, but it is best to use less, have to use the difference 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;
Note: Both IE and 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;
IE6 IE7 FF
* √ *
! Important × √
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Add another underscore "_",
IE6 supports underlines, while IE7 and firefox do not.

So you can also distinguish IE6, IE7, and firefox.
: Background: orange; * background: green; _ background: blue;

Note: No matter what method, the order of writing is firefox's preface, IE7's writing in the middle, and IE6's writing at the end.