By chance I took a look at the Stories page using Chromium, and since it's missing decoding capabilities compared to Chrome, a Vimeo error message is shown when trying to load videos. (see screenshot)

I think we should provide fallback images and load videos asynchronously. This would show something for all browsers, and give the video to browsers that support it.

In Firefox for instance the videos are loaded but they're not started, meaning you see a black box during loading and it feels really sluggish, but all you get in the end is a static image. With fallback images you'd get the same result much faster.