It works in 1.1.7.2(previous release of this addon) with the latest firefox version.
You can open download panel through toolbar.

The button under the player is hidden again, but it is possible to call the download panel from the button in the toolbar of the browser.
If the download panel doesn't finish loading, lowering the version to 1.1.7.2 may help.
By the way, the download speed issue has also been resolved since 1.1.7.2.

(The above is a translation of Japanese into English using Google Translate.)

me encanta, lo mejor que he tenido en este tipo de app

This is generally an excellent product, but as others may have said, the latest version is for some reason not working (perhaps due to an update in YT's UI), but you can go back to the versions page and download an earlier version that appears to be working normally. I'm having good results with Ver 1.16.

[update 1.17.2022]
- for me 1.1.8 doesn't work, reverting to 1.1.7.2 does.
- Slow DL speeds?
For months my file download speeds have been capped at <100KB/s, don't know why, and I just happened to completely remove the addon today, reinstall it, and now the download speeds are full bandwidth again! Don't know what the problem was, but try that if your DL speeds suck for unknown reasons. For months I assumed it was YT changes, but the 'Easy Youtube Video Downloader Express' ext gave me full DL speeds, except that ext sucks because they paywall most of the DL links, and make a scam claim that they charge money because they do "processing on their server infrastructure". A BS claim, when THIS ext built on opensource code gives you ALL the DL links, for free.

[Review 6-24-2021]
This awesome extension is regularly broken by either Firefox updates or YouTube back-end changes. Kudos to the dev that maintains it!

Stop being surprised when it breaks - and remember - people respond quicker and are more likely to fix something if you ask nicely, especially when they do it for free.

YouTube doesn't support this extension existing, because they charge to "download" videos, but only to select devices in limited fashion, inconveniently. So YouTube makes changes without regard to breaking this, or intentionally break it. And Firefox updates never help.

[older issue that probably still has something to do with youtube breaking it regularly]
Apparently 10-23-2020, the RIAA filed a DMCA takedown against the code repositories, used by extensions like this, to download YT videos. Cause "piracy".

Here's more info:
https://www.xda-developers.com/youtube-dl-riaa-dmca/

new updated version is not working yet. i am sure it will get fixed. in the mean time, i downloaded the last stable version and it works fine. i will update once i see the bugs are worked out. don't rate the app 1 star if you can't figure out to remove and reinstall with last working version. not fair to the developer of this great extension. thanks mate for this tool.

**STOP COMPLAINING YOU PEOPLE**
Download the previous version: 1.1.6 for the time being
This extension is the best YT downloader I've tried.
As YT changes their codes from time to time, it did mess up this extension.
You guys should pay a lot of respect to the developer as they always find a way to fix that in a matter of days.
I always JUST sit back and relax and WAIT.

I have used this for Many Many years and it has been Great.

At the Moment Version 1.1.8 The Hour Glass either freezes or just keeps spinning.

Rolling back to 1.1.7.2 has fixed it, I was getting slow downloads for months with this version, but after quite a few attempts at completely removing and reinstalling, it now seems to be downloading properly again.

大家用旧版1.1.7.2 就可以了You can just use the old version 1.1.7.2 去作者主页找历史版本 然后下载 1.1.7.2版本 不能下载问题 完美解决Go to the author's homepage to find the historical version and download 1.1.7.2

These are the hardest working devs on the Internet. I have been using this plugin forever, and it has worked 90% of the time. The other 10% is YouTube's fault for changing things up, but these guys are always on TOP of it, man. For now, going back to 1.1.6 will fix most of your issues, until they get to the new problems. Just go back to the main page, under "More Information" box, under "Version History" click on "See all versions" and find 1.1.6 and click that download link.

TO FIX THE PROBLEM, I went back to version 1.1.6 which also uses the older detection algorithm and that works great for me (five stars great). Other users may want to do the same until the bugs are worked out of the latest release. I also set it to NOT automatically update for now since I don't want 1.1.6 to be replaced by that buggy new version. Once the bugs are fixed, I'll set it back to the Default value again.

VERY GOOD

At the moment ,there's a bug , started a day or so ago. When trying to download the WebExtensions process goes nuts using 98.7% of the resources. Normal browser behavior returns when that process is killed. Hope it helps. When it's functional , this is the greatest extension and i use it all the time. Thanks.

I've used this for years and it usually works flawlessly. Every once in a while it stops working for a while, probably because of a change by YouTube, possibly a change by Firefox. But so far it's always gotten fixed eventually so I'm optimistic that the current problems will get fixed. Thanks to the developers!

This problem (freeze of download panel) also occurs in Firefox ver.95.0.2. Youtube may have changed the specifications.

(Translated into English by Google Translate. I'm sorry if the nuance is wrong)

非常好用