I have a very simple way to speed up sending email messages from Gmail for users of Firefox and other browsers which feature a sidebar. to add this in Firefox simply create a new bookmark (right click the bookmarks toolbar and select new bookmark). the two important paramaters here are the url for the simple gmail compose window (eg the one with out the gmail sections selectors), this url is:

http://mail.google.com/mail/?view=cm&tf=1&fs=1

to open it within the Firefox sidebar, you should select the 'Load this bookmark in the sidebar' check box. Note that the compose window is fairly wide so you may have to increase the width ot the sidebar so that the currently viewd page is fiarly small.

To do this in Opera simply drag the above link to the Panels menu (if you don't see this press f4), and the link will load in the sidebar (although you could just use the Opera mail client m2, which is built in to Opera)