“I’m always looking for ways to save time. Suppose I want to attach some files to an email, and I already have a folder open containing those files. I used to have to click “Attach a file,” find the photos, click them, etc. Starting today, if I’m using Google Chrome or Mozilla Firefox 3.6, I can just drag and drop the files to attach them — easy as pie.
We’ll enable this for other browsers as soon as they support this feature. For now, you can drag and drop attachments in Chrome and Firefox only. ” Gmail blog