Chrome 15 had labs feature called Side Tabs which doesn’t reached the Stable version though (that’s why there are called experimental feature) useful for wide screen monitor users which enables vertical tabs. If you want that feature in Firefox there is Side Tabs extension.
Side Tabs for Firefox Extension
Features
- Moves tabs to the side of your screen
- Easily manage 30+ open tabs
- Great for widescreen monitors
- Position on the left or right side
- Adjust width to your preference
- Restartless Firefox add-on