firefox 3 on ubuntu 8.04 on amd64 system: embedded youtube video on web sites are completely invisible

[RonaldH]

Binary package hint: firefox-3.0

Situation:
amd 64 system
ubuntu 8.04 amd64 (original download from ubuntu web site) apt-cache
firefox 3

Problem:
youtube video embedded in web site not visible
sample:
the video on youtube (works perfect):
http://www.youtube.com/watch?v=WnhuKs459J4

the sample web page (at the very bottom, invisible):
http://www.webdesign4uonline.net/services-de.htm

the same problem also appears on other web sites

ProblemType: Bug
Architecture: amd64
Date: Fri May 16 13:52:47 2008
DistroRelease: Ubuntu 8.04
NonfreeKernelModules: fglrx
Package: firefox-3.0 3.0~b5+nobinonly-0ubuntu3
PackageArchitecture: amd64
ProcEnviron:
 PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: firefox-3.0
Uname: Linux 2.6.24-16-generic x86_64