Rated 3 out of 5 stars

Doesn't work at all in Firefox Dev (no more drop down menu), and downloads 0 Ko files in Firefox 51.
Edit: Thanks for the reply. Will donate as soon as fixed ;)
+ please allow typing of the path to ffmepg instead of a button, as macOS file navigation is a real pain to get to usr/ for non advanced users.

This review is for a previous version of the add-on (5.7.29). 

Working on this now...