其实题目不太确切，应该是对回车(Return，即r)换行(New line，即n)的不同处理
看示例就明白了：
其中pre的部分参考上一篇文章
IE和Firefox对换行的不同处理
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<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
<script type="text/javascript">
<!--
function removeLineBreaksIE() {
var testDiv = document.getElementById('test');
var text = testDiv.innerHTML;
testDiv.innerHTML = '<pre>' + text.replace(/rn/ig, '') + '</pre>';
}
function removeLineBreaksFx() {
var testDiv = document.getElementById('test');
var text = testDiv.innerHTML;
testDiv.innerHTML = text.replace(/n/ig, '');
}
//-->
</script>
</head>
<body>
<div id="test">
<pre>
line 1
line 2
line 3
line 4
</pre>
</div>
<button type="button" onclick="removeLineBreaksIE();">Remove line breaks for IE!</button>
<button type="button" onclick="removeLineBreaksFx();">Remove line breaks for Firefox!</button>
</body>
</html>