[SOLVED] Mythweb/MythVideo reports 500 Internal server error using Firefox for MP4

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http://ubuntuforums.org – MythTV v0.26.1 ubuntu LTS (x86_64) Firefox 23.0 with addon: HTTP Live Headers VLC plugin 2.0.8 Twoflower installed I'm trying to view a *.mp4 movie created with Handbrake 0.9.9 rev0 using Mythweb's MythVideo, but nothing happens. Why does Firefox display the error message "File not found" and the HTTP response header reports "HTTP/1.0 500 Internal Server Error" ? Why can't Firefox play an *.mp4 movie? Here are the headers from the HTTP request using Firefox as the webbrowser: GET /mythweb/video/stream?Id=1 HTTP/1.1 (Hardware)