With high-res, widescreen monitors, it makes a lot more sense to have tabs in a vertical stack. Check out Tree Style Tabs for Firefox: https://addons.mozilla.org/en-US/firefox/addon/tree-style-ta...

This is the must-have feature that keeps me using Firefox -- especially when I'm doing research, which has a naturally tree-like pattern. Apparently, from the Chromium bug, it's a dealbreaker for lots of other people as well: https://code.google.com/p/chromium/issues/detail?id=344870