The video works only in Firefox because many moons ago video playback was done via software installed on the system.

Either via Windows Media Player Image

Apple Quicktime Image

or other video playback software that came with web plugins like Realvideo.

This of course created a mess of inconsistency, and so eventually Adobe Flash Player and Java (Applets) were used to create platform-independent video players that the website embedded.

As the video used the before-Flash way, Firefox is able to extract the video URL and play it like a video playback plugin is present. Chromium simply didn’t implement this and decided to just error out for being deprecated.