The WordPress editor window is somewhat odd if you are writing in text mode but need to scroll down to preview your post. From several blog editors that I have tested now – there is now one that made it onto my desktop. Scribe Fire is an advanced Firefox plugin that can be nicely configured as you can see on this screenshot.
The “powered by” can be switched off by clicking on the left >>, followed by Settings > General > Publishing Features.
Take care that while configuring your account that you select Manually > Custom Blog > WordPress (instead of selecting wordpress.com).