I really Like Firefox because of useful add-ons. There is Firefox add-on that will support drag and drop in wordpress editor. I think it is much needed feature of wordpress but it is not possible in core wordpress setup in any plugin but it is Firefox that has made it possible. I use Windows Live Writer to compose my posts.
Now doubt browse feature in wordpress editor is very slow specially on slow internet connections. So if you have installed this add-on you word is done.
This add-on is not just for Firefox it supports Gmail for add as an attachment via drag and drop, however, you can sue it for Google Docs too. however Google docs support drag and drop feature by itself. You can drag and drop multiple attachments. You also can use this add-on to drag and drop test snippets.