I'm a Gmail fan too, I would like to share with you all one of my favorite Gmail firefox extension which allows you to use your Gmail Space (2.5 GB) for file storage.
Gmail File Space Extension (gspace)
This extension allows you to use your Gmail Space (2 GB) for file storage. It acts as a remote machine. You can transfer files between your hard drive and gmail. This is similar to "Gmail Drive" on windows platform. Your gmail account looks like a FTP host and you can upload and download your files. After you install, you get an option called "GSpace" in your "tools" menu clicking on which opens the window for transfer of folders/files.
Download it here ...