Awesome Add-on! I'm using this one for yrs and it works tremendously. Every now and then, after some YT or OS/Browser changes it did not work for a couple days (I think the longest was about 2 weeks) but after the next update it worked fine again. The recent pathname error was fixed with Version 1.1.2 and despite some claiming it didn't work on music vids anymore it actually does work. Tested it and had no issues with any vids so far. Thus I wrote this updated review.

Update 6.12.2020:
Concerning review from Rastan / 06.12.2020
I had exactely the same experience these last 3 days. Tried installing older versions also combined with older Firefox ver. but always ended up with the same error message so far. I trust that the add-on is fixed as usual within a reasonably short time. I'll keep updating this review when it's fixed or in case the problem should persist.

Update 7.12.2020:
Addy works again. Haven't tested widely yet but a quick test showed I could dl and chose the format I wanted this morning again. Will update again if necessary. Thanks to others who update their reviews too and sometimes share tips how to circumvent a problem for the time being.

Update 8.12.2020:
Doesn't work again now. The same friggin error shows up. To the dev of this addy: I'll wait like always till you fix it, this tool is just soo effective when it works that I really have no intention to change the addy as long as problems are fixed within days.