When you create a flash object, it saves it with the mime-type image/vnd.rn-realflash, which seems to be correctly loaded only with Opera but not with Firefox 3 (Mac and Windows), IE7 and Safari (I have tested all the most recent versions and plugins).

My temporary solution:
remove from mime.ini the lines under [swf] block

Types[]=image/vnd.rn-realflash
Types[]=application/x-shockwave-flash2-preview

leaving only:

Types[]=application/x-shockwave-flash

This way the swf objects are saved with the right mime-type and are loaded in IE7, Firefox and Safari.

Steps to reproduce

Publish a Flash object and try to load it in IE7 or Firefox 3 with Flash Player 10.