Rated 4 out of 5 stars

Perfect extension for any Markdown user. I use it with SublimeText and AutoReload extension (https://addons.mozilla.org/en-US/firefox/addon/auto-reload/). Would be good to have an option to define your own CSS path.
By the way, it works under OS X, at least I haven't felt any bad consequences yet. Interesting why the developer has decided to leave OS X out after 1.1 release.

This review is for a previous version of the add-on (1.2.1-signed).