If you don't configure the server to use https it's not possible to send mail from firefox and roundcube 0.2 (stable and svn). It works from IE7 but not in FF 3.0.X. Pressing the "Send" or "Send now" button has no effect at all.
When enabling https on the server everything works. I don't think anyone should run this without https, but it could be mentioned in the installer as a requirement.
Tom