overflow-x: auto problem on firefox/ie

Answer 1

No this isn't specifically an overflow-x: auto problem. It is is caused by elements with width: 100% interacting with fixed width elements elsewhere on the page. In the case of SO's #footer, it is width: 100% (implicitly), whereas the #content is declared width: 960px.

When the page width shrinks below 960px, the #content's width forces the browser to add a horizontal scrollbar (implicit overflow-x: auto). Since the #footer is set to 100% width, it only expands to 100% of the viewport, and the section beyond the scrollbar doesn't get the background color properly added.

To fix this, you can add a min-width declaration to the css:

#footer {
    min-width: 960px;
    /* other css goes m'ere */
}