16. Why does Firefox load my SWF twice?
Firefox 3 has a known issue that sometimes causes a swf to be 'double initialized'. The problem appears to be fixed in their codebase, but has not been released yet. See the following bugs for more details: bug 438830 and bug 445599.
Or, if you have "Disable cache" selected in your Firefox Web Developer Toolbar extension a double load will occur.
SWFObject_2_0_documentation Embedding Adobe Flash Player content using SWFObject 2.0