Firefox only: Gmail's powerful filters and labels make it great for organizing, but when you have multiple labels assigned to a message the subject barely fits on the screen—unless you auto-hide them with a script.
The simple Hide Message Labels in Gmail script changes the labels to only display when you move your mouse over the message, letting you use labels for organisation without cluttering the display—especially useful for using Gmail on a smaller screen resolution display.
Hide Labels in Message Row is a free download, requires Firefox with the Greasemonkey or Stylish extension. If you are a fan of minimalism, you can use a user script to hide the footer and other clutter in Gmail along with the Better Gmail 2 extension to customise even more. Thanks, Hervé!
Gmail - Hide Labels in Message Row [userstyles.org]