Greasy Fork is available in English.
Adds a progress bars (or dots) at bottom of video, a progress text which includes video quality and subtitle indicators, and a chapter title box on the YouTube video page.
< Spätná väzba na Add YouTube Video Progress
That's a known problem from my perspective. But since the new interface is shown randomly, it's difficult to reliably test it. Moreover, the new interface design seems to not yet finished - as changes are still being applied quite frequently.
I think there are some issues with the new interface.