Awhile ago, I mentioned Mozilla’s Prism which allows you to run websites in a manner which more closely resembles a desktop application within a standalone window. When using $g(GMail) the default Rich text editor for the message body doesn’t work and the editor appears read only. The key is to click the “Plain Text” link and switch the editor style which will allow you to type your message.
Since Prism was initially released I haven’t heard/read anything else about it’s development so hopefully we’ll see improvements/fixes. If you haven’t at least played with Prism I highly recommend.