problem with visual editor width on firefox

i jump in this conversation to report a similar issue: when I type text in the visual editor, the text doesn’t get wrapped up but it keeps on expanding endlessly on the right side when using Firefox. Look here:
http://www.freereporter.info/it/2013/03/14/land-and-safe-food-are-they-available-to-all/
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http://wordpress.org/extend/plugins/wp-user-frontend/