Mou's live preview was neat for about a week, but eventually I just switched to Sublime Text with the MarkdownEditing, Markdown Preview, and Markdown TOC packages. Powerful stuff, and as-good-as-live preview in your browser.

https://sublime.wbond.net/packages/MarkdownEditing https://github.com/revolunet/sublimetext-markdown-preview http://dotcypress.github.io/GitHubMarkdownPreview/