Not the official version... https://addons.mozilla.org/en-US/firefox/addon/free-download-manager-addon/

good but should be faster

Using firefox quantum 61.01.
When this addon is activated I notice
continued outbound connection attempts
to coinhive.com. Coinhive is a Trojan Data Miner
that severely compromises your compuer.
When this addon is deactivated the connection attempts
stop. Draw your own conclusions but the addon does not
function with Firefox Quantum other than to attempt
this connection. Google coinhive.com for further details.

下载中文时候，名称出现乱码

complicated setup and it wont feed FDM with password, which is unhelpful.. funny how these browser integrations worked 10 years ago and suddenly everything is a problem.

Doesn't work on my Mac

Installed the firefox add on, installed the fdm from fdm page, went to a web page where a number of song sheets in pdf were available for individual downloading. could not get fdm to do anything about downloading these pdfs.
How I miss DownLoadThemAll. It never failed.

Doesn't work with Firefox Quantum.

If you feel this extension no longer work for you, try this extension instead:
https://addons.mozilla.org/firefox/addon/free-download-manager-addon/

Can't catch Firefox quantum download link

Doens't work on Firefox Quantuum

Doesn't work with current version of firefox. Use to be a must have app but not anymore if you count on using firefox.

I stop using Firefox all together. Firefox has been my default browser since 2004. A working integrated download manager made this browser the best on the net. Now, many people are ditching Firefox because of a real lack of interest from developers to fix FMD functionality. Saying that... bye bye Firefox.