Firefox could be picky with the html. I see you have more than 1 flash item on that page, using the EMBED tag. All those show just fine, but you enclose those EMBED tags with the OBJECT tag as well.
If those flash items display fine, maybe you should follow the same coding to display the flash games.
Just look at the html of that page, and search for EMBED and you will see the other embed tags used on the page.
Like the visubox on the left, for example:
<embed src='/forum/visubox/visubox.swf?p=/forum/visubox/&utf=0' scale='noscale' menu='false' width='150' height='280'
name='visubox' type='application/x-shockwave-flash' pluginspage='http://www.macromedia.com/go/getflashplayer' ></embed>
Currently the EMBED code for the flash games is this:
<EMBED SRC="http://www.giumer.it/forum/flash/flash_poker/flash_poker.swf" WIDTH="550" HEIGHT="400"
HIDDEN="false" AUTOSTART="true" LOOP="true" volume="100"></EMBED>
Couple things you could try.
- Use lower case tag and attributes
- add the TYPE attribute: type="application/x-shockwave-flash"
And let us know if it works.