Reinstall the YouTube downloader Firefox extension and then update it by going to Add-ons then Gear and click on Check for Updates. I hope it will solve your issue. Please let me know if it works or not.

Thanks very much Naheed. I followed your solution instructions, and they worked a treat. The green download button has finally reappeared on Youtube, and that was the main issue I was having trouble with. I really appreciate all of your kind assistance to help me out. Regards,

Phill.

Was having the same problem. Followed instructions, got the green bar back but is not working. Any suggestions? Thanks, Keith

Fresh install running FF 93.0 64 bit. on linux I removed and reinstalled and finally got the prompt to allow the add-on to access FF. Now the green download button has reappeared!