No options to dowload from youtube

When I open a video on youtube, I can't download the file as SFN button does not give me any options. Screenshot attached is self-explanatory I think.

I can't say for sure but ithappens more often on age-restricted videos, as some other videos download just fine.

Besides, I was able to download that video through the sfn web-site. Add-on however doesn't work.

More browser info:
Browser: Firefox 77.0 Mac OS X
User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:77.0) Gecko/20100101 Firefox/77.0
Extension: ff 8.92