Free Download Manager official extension v3.0.64 
It's an official Firefox extension by Free Download Manager developers. The sole purpose of this add-on is integration with FDM.
FDM is a fast and reliable download manager and accelerator that improves your experience with downloads and helps you organize them in an easy manner.
It works on Windows and macOS and features a user-friendly interface with modern design. FDM allows video downloading from popular websites and supports HTTP/HTTPS/FTP/BitTorrent download protocols. Also, it can boost all downloads up to 10 times, efficiently process large files and download multiple files at the same time.
With it, you can drag&drop links from a web browser, preview audio and video files before downloading, convert files to desired formats, etc. For faster download processes, split files into several parts that are processed simultaneously, resume downloading after the connection loss and schedule downloads to be processed at the convenient time. Get full control over the traffic usage and downloaded files.
If you want to help us make Free Download Manager (or this Firefox extension) better, you are always welcome to our forum where you can post bug reports and feature suggestions as well as get support for any issues you stumbled upon with FDM: https://www.freedownloadmanager.org/board/
Note: Windows, Mac and Linux! Requires FDM to be installed to work properly.