Containers	Chromium	Mobile Chromium	Edge Chromium	Firefox
3g2	✓	✓	✓	✓
3gp	✓	✓	✓	✘
avi	✘	✘	✘	✘
m2ts	✘	✘	✓**	✘
m4v etc.	✓*	✓*	✓*	✓*
mp4	✓	✓	✓	✓
mpeg	✘	✘	✘	✘
mov	✓	✓	✓	✓
ogm ogv	✓	✓	✓	✓
webm	✓	✓	✓	✓
mkv	✓	✓	✓	✘

* Container might be supported, but the container's codecs might not be.
** Documented as working, but can't reproduce.
Full list of all tested video extensions:
.3g2 .3gp .asf .avi .dv .flv .gxf .m2ts .m4a .m4b .m4p .m4r .m4v .mkv .mov .mp4 .mpd .mpeg .mpg .mxf .nut .ogm .ogv .swf .ts .vob .webm .wmv .wtv
Are any missing?

Video Codecs	Chromium	Mobile Chromium	Edge Chromium	Firefox
AV1	✓	✓	✓	✓
H.263	✘	✘	✘	✘
H.264	✓	✓	✓	✓
H.265	✘	✘	✓*	✘
MPEG-2/4	✘	✘	✘	✘
Theora	✓	✘	✓	✓
VP8/9	✓	✓	✓	✓

* Requires MSStore extension which you can get by clicking this link while using Edge.

Audio Codecs	Chromium	Mobile Chromium	Edge Chromium	Firefox
AAC	✓	✓	✓	✓
AC3	✘	✘	✓	✘
DTS	✘	✘	✘	✘
EAC3	✘	✘	✓	✘
FLAC	✓	✓*	✓	✓
MP3	✓	✓	✓	✓
Opus	✓	✓	✓	✓
TrueHD	✘	✘	✘	✘
Vorbis	✓	✓	✓	✓*

* Might not work in some video containers.