I've converted the file to three different formats: mp4, web, and ogv. According to caniuse firefox supposedly supports both ogg and webm, but nothing is playing.
I converted the files using Miro Converter, according to other people this should work just fine. I believe Chrome picks up the webm file (if i rightclick -> open in new tab, it shows me the webm file), which is great.
URL to the site: http://dev.fristil.se/hbh/
I have a static image as a background. The video is suppose to display above it, so if it's not moving you can tell it's not working.
Any ideas?
Your server is not sending the correct mime type for the file.
It send Content-Type: text/plain
The HTML5 video may play in Safari, Chrome and IE 9 but not Firefox or IE 7-8. If you fix the MIME-type issue, it will play in Firefox.
If you’re using the Apache web server or some derivative of Apache, you can use an AddType directive in your site-wide httpd.conf or in an .htaccess file in the directory where you store your video files. (If you use some other web server, consult your server’s documentation on how to set the Content-Type HTTP header for specific file types.)
AddType video/ogg .ogv
AddType video/mp4 .mp4
AddType video/webm .webm
AddType audio/mpeg .mp3
AddType audio/ogg .ogg
AddType audio/mp4 .m4a
AddType audio/wav /wav
You have same question here: Video file .ogv plays locally in Firefox, but not from server and more detailed answer: https://stackoverflow.com/a/6145629/1081079
Your problem is server-side. The server is actually returning text/plain as MIME type for the videos (at least the .ogg one). You will need to adjust your server's configuration to return the correct MIME type so that Firefox can correctly recognize the file. It is the same issue described here: no video with supported format and MIME type found. What does this mean and how can I change this (you just don't see the message because you don't have the controls option in your <video> tag).
Your server delivers the resource http://dev.fristil.se/hbh/wp-content/themes/skal/images/video/bubblybeer.webm with the HTTP header Content-Type: text/plain – and therefore Firefox refuses to treat it as anything else.
“Teach” your server to deliver such content as video/webm.
(Same goes for your ogv – your server also says that resource would be text, should be video/ogg instead.)
I was having the same problem w/ webm using the Flowplayer HTML5 player. Firefox said "HTML5 Video Not Found". At first I thought it was Miro having an encode problem and I tried several different programs, all with the same result. So I narrowed it down to either an improper MIME type on my server, transmitting the webm as text/plain (you can use web inspector to see this) or Firefox just sucking. I had the hosting provider AddType video/webm .webm a while ago, so I can't be positive. What I did was just remove the webm reference directly from my HTML after realizing that I had used Flowplayer in the past and only needing a single mp4 file. Firefox can use mp4. Remove this:
<source type="video/webm" src="URL_to_webm.webm" />
That made it work on everything (IE, Chrome, Firefox, iPad, iPhone). Chrome 29 on Mac uses the mp4.
I got the same problem in my windows hosting. To solve this i included the mime setting in web.config inside
<staticContent>
<mimeMap fileExtension=".webm" mimeType="video/webm" />
</staticContent>
来源：https://stackoverflow.com/questions/15656465/html5-video-not-playing-in-firefox