Try seeing if setting a height helps show the video. FF can be... quirky about that, refusing to auto-calculate an appropriate height.
Silly question -- what codecs are you using inside those containers? Is your .webm VP8 or VP9 video?
Remember, .webm, .ogg and .mp4 are just container formats, and can contain different encodings that may or may not be supported.
Check the MDN reference on that:
I just checked, your OGG file isn't big enough to contain video, and seems to just be a vorbis AUDIO stream. For some reason FF and Opera here are using that video-less OGG file skipping right over the .webm file.
I do think the mime-types are messing with it; they're NOT being sent properly.