Your web server appears to be sending a content-type of text/html for .php automatically, so I'm not sure why adding a meta tag would make any difference. ??? (Note that it's content-type in all lower case.)

Your web server also is sending audio/ogg as the content-type of omen.ogg. Perhaps the server is configured to send video/ogg only for .ogv?

See also:

• https://developer.mozilla.org/en/Configuring_servers_for_Ogg_media

gzip deflate compression is not the answer because the test video for the html5 video tag from the w3c web site played just fine in Firefox without gzip deflate compression being turned off.

Do you have a test page that has the meta tag for comparison?

The test page I have now has no meta tags at all. According to Firefox accepts gzip deflate compression by default. Therefore it is always on. If you look at this test page http://www.lclaasacramento.org/testVideo.php it works. The server has the correct memi type in the configuration file

Note that compression used on media files can cause problems if there is only part of the file in the cache.
If the file is fully loaded the this shouldn't be a problem.
If not then there may be confusion on how to interpret from which file range to start (byte count of the compressed file or the uncompressed file).