View source to show the code CSS behind these first two PRE examples.

A pre with no changes other than border to highlight the box. It should scroll off the side of your browser, because there's no line wrapping on line 4 and it's long. This renders the same on IE7 and FF3. 

line 1
line 2 
line 3
line 4: This is a long line. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Donec placerat, leo vestibulum aliquet auctor, lorem dolor venenatis nulla, sit amet lobortis leo enim et dolor. Duis ut urna vitae dolor scelerisque sagittis. Curabitur magna. Sed nulla. Ut metus. Etiam interdum.
line 5
A pre with the same exact content, but with some overflow changes: 
line 1
line 2 
line 3
line 4: This is a long line. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Donec placerat, leo vestibulum aliquet auctor, lorem dolor venenatis nulla, sit amet lobortis leo enim et dolor. Duis ut urna vitae dolor scelerisque sagittis. Curabitur magna. Sed nulla. Ut metus. Etiam interdum.
line 5
However, if we wrap the pre tag in a div and set the overflow and other properties on it instead of the pre, then scrolling works. Am I doing something wrong, or are pre tags somehow skipped when deciding to grow them to support a scrollbar? 
line 1
line 2 
line 3
line 4: This is a long line. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Donec placerat, leo vestibulum aliquet auctor, lorem dolor venenatis nulla, sit amet lobortis leo enim et dolor. Duis ut urna vitae dolor scelerisque sagittis. Curabitur magna. Sed nulla. Ut metus. Etiam interdum.
line 5
On my windows box (IE 7 / Vista Home Premium) the above pre looks like the following. Notice how the 5th line is not displayed, clipped by the new horizontal scroll-bar:

Firefox does what I want, only horizontal-scrolling and not clipping the last line with the scrollbar: