Firefox Error - Cant Download Uncommon File Type

&q=youtube+downloader+firefox

How to fix the problem of Firefox not downloading "uncommon file types".

Since Published At 10 04 2017 - 18:15:09 This Video has been viewed by [VIEW] viewers, Among them there are [LIKED] Likes and [DISLIKED]dislikes. This Video also favourites by [FAVORIT] people and commented [COMMENTS] times, this video's duration is [DURATION] mins, categorized by [CATEGORY]

The video with titled Firefox Error - Cant Download Uncommon File Type published by Larry Pike with Channel ID UC9tt2z-thj6LD9vv8MDIRvQ At 10 04 2017 - 18:15:09