From the Firefox addon store:
> DeArrow is a browser extension for YouTube for reducing sensationalism, misleading titles and aggressive thumbnails. DeArrow works by formatting all titles, and replacing thumbnails with screenshots at specific timestamps.
> No more dealing with clickbait, arrows, or annoying faces.
> Users can submit better titles and thumbnails for each video and vote on them.
> replacing thumbnails with screenshots at specific timestamps
so in other words bringing YouTube back to the better. I think there was a point in time in the past where creators were not able to upload custom thumbnails and instead they could only use the select thumbnail from time feature or perhaps even the thumbnail was automatically chosen. I don't quite remember.
It's funny because I have actually found that making good thumbnails really is challenging. I run a PeerTube instance of my own where I host some videos and in general even though I tried to put some effort into making useful thumbnails by hand I think my handmade thumbnails are not very good and it's better to just use some frame from the video itself as thumbnail.
I remember at one point it used the thumbnail that was at exactly 50% of the video. So some creators would cut their videos to intentionally select a specific frame.
The readme is super vague and only describes install instructions..