Rated 3 out of 5 stars

Simply open a markdown file with an ".md" extension and it renders nice-looking formatted text. It even gets accents and other Unicode characters right. Unfortunately, because this is a legacy add-on, it disable's Firefox's multiprocess feature: if you go to "about:support" while this add-on is enabled, you'll see that the number of Multiprocess Windows is zero.

This user has a previous review of this add-on.