Give the ability to have the preview pane beside the edit form.

Note: Replace or add to the url-prefix your own Redmine URL (must be done at each update, new settings system could prevent this):
@-moz-document url-prefix("http://www.redmine.org/"),
url-prefix("http://my.redmine.url") {
...
}

Changelog (26/08/2010):
- First version.