[trunk] horizontal resize incorrect on Firefox 3.6.5

[Ruud Riem-Vis]

Create a new db with CRM installed. Log in and select the sales section.
Now extend the window horizontally on the left or on the right. When you exceed the maximum width of the top banner, the banner will end but the content continues to extend on Firefox 3.6.5. The behavior is ok on IE 8.0

Probably related, select from "sales" the submenu "configuration->product->product categories". Now when you extend the screen on Firefox, the content part will stick to the right side of the window and the horizontal scroll bar will never disappear (even when the screen is big enough).

On IE 8.0, the horizontal scroll bar disappears when the width is large enough but the content is shifted far down when the window is resized to become smaller in width so that the scroll bar appears.

I can provide screen shots if required