I tried with two different browsers (Firefox 11, Chromium) and both have the same problem. My OS is Ubuntu (10.10) with kernel version 2.6.33. In Firefox and chromium i use the following (IMHO relevant) extensions/plugins:
IcedTea6 1.9.13 (open source Java replacement)
Shockwave Flash 11.2 r202
I searched the forum and the web, but couldn't find anything related. Thanks for any pointers.