Gmail is an absolutely awesome product and I personally believe it revolutionized the world of free web based email clients.
However every now and then there is some little feature or functionality you just which you had. The GMail team is doing a great job of adding features but they can't do everything right away. Fortunately a bunch of FireFox extension hackers got together and made tweaks for things they found annoying; they then bundled them together and offered the package to the world.
Hopefully all the ideas in this extension will eventually made it into the native GMail interface, but until then it is one extention that makes the GMail experience much cooler. Check it out here:
GMail FireFox Extension