Theme Tweak: Sidebar layout: Fixed story, fluid sidebar
(regular 14" monitor)

The issue is this CSS in vanilla / base.tid:
.tc-menu-list-item {
white-space: nowrap;
}
Imho, neither should the description be forced on one line, nor should it be on the same line as the label.
may be:
.tc-tab-content.tc-vertical {
overflow: auto;
}
will help to
It does. However, I guess horizontal scrolling is possibly among the top entries on a web-designer's don't-list, Btw. kudos for the Firefox plugin.
horizontal scrolling
yea ... may be overflow-x: auto may do the trick too.
Thanks @pmario @tobibeer a fix would be welcome - as far as I know, this problem affects all content within vertical tabs.