And here is the updated (2005) Mozillazine Embedding thread:
http://forums.mozillazine.org/viewtopic.php?t=206216
And here's an interesting bug report:
Effects
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FireFox v1.5
Windows Media Player v10 (and 9.0)
Issue
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When creating the <embed> tags, there are a number of attributes ignored by FireFox. The most annoying one is AutoPlay. By default, FF plays all videos period. There is no option to disable a video/stream from playing when the page loads by setting this to False, 0, etc.