Firefox and xvid .avi

I’m trying to move to Firefox after Chromium lost its sync feature, and it largely works, but I can’t seem to make it play xvid videos.

I don’t have link permissions, but specifically the type listed as MPEG4 at

xvidcore is installed, and if I download the .avi file that can’t be played ( ffmpeg can decode it just fine. Chromium plays it properly, but Firefox doesn’t.

What am I missing?

:+1: Welcome to Manjaro! :+1:


MP4 / MEPG4 videos were handled by plugins in the past but none are available any more

The long version:

Back when Firefox was still called NetScape, videos were handled by animated GIFs and videos with audio were handled by the QuickTime plug-in from Apple.
A bit later they were handled by Adobe’s Flash player, and nowadays they’re being handled by HTML5, so Mozilla never bothered to include a native MPEG4 video player because MPEG4 has patents associated with their technology and Mozilla is and always has been very much open source.
So now that Adobe’s Flash player has gone the way of the dodo is not available any more, no one else bothered to write a new plug-in and Mozilla doesn’t want to touch it with a 10-foot pole.

Having said the above, most modern websites use HTML5 to play videos and only old, crappy unmaintained websites still use MP4, so although there is now a glaring hole in FireFox, it won’t matter much to you. (I haven’t run into any websites like that in years!)

Google, having deep pockets and lots of lawyers, just wrote their own native MP4 decoder (and probably paid the patent fees to the Motion Pictures Group. ( .MPG was the original file extension)


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Hey, maybe something like this could provide an acceptable workaround?

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I’d say:
a browser is not a video player

You use a browser to download a video.
You use a player of your choice
vlc, mpv, mplayer … or any other tool based upon these
to play back the downloaded file.

… goes along with what @BusinessOrc said
which then might turn your browser into a video player of sorts
even though you likely have installed at least one proper video player already

That was my misunderstanding too at first, bit YouTube, Vimeo, … are all examples of sites that did move to HTML5, but there are still crappy sites out there that never made the move…

That’s what the question is about…


but if the site is just providing the (.avi) file
but not a player to serve/play the file

then just download it
and play it from local storage
with the player of your choice

the benefit is
that you’ll never have to download it again if you want to re-watch it
this isn’t the case with embedded players, serving the file.

This is also the reason for browser extensions like “video download helper” or “youtube downloader” or others to exist.

to download the file once - instead of over and over again when you want to re watch it.