For whatever reason when zooming on StephenFry.com the left edge of content ends up outside the Firefox viewport when zoomed in, and the scrollbar doesn't extend such that I am able to scroll left. Other sites behave normally, with the left hand content always staying in frame.

This happens because the site uses a stupid way of "centering" the content which is just broken at narrow window widths. It puts it all in a div with these styles: width: 960px; position: absolute; left: 50%; margin-left-value: -480px; Any time the window width is less than 960px (and zooming changes the size of a "px" in this context), the content will stick out the left side of the window. The lack of ability to scroll to content overflowing to the left is bug 6976.