The editor (nsEditor, even) has a method called GetWrapWidth which checks the pref editor.htmlWrapColumn. But then that value is never passed to the serializer, so there's no way to turn off wrapping or wrap at a value other than 72 columns. This may be related to bug 236290, in which the html serializer ignores its wrap flag. But it actually does take the passed-in wrap column setting, so this bug may not be dependant on 236290.
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