Well. it's somewhat ridiculous, but I finally got the CMIVFX player to work.
Not in the "supported" browsers "Google Chrome" or "Firefox 4 beta", but in "Firefox 3".
There is still one drawback.
While "Firefox 3" loads and plays the content nicely, I still have to use "Google Chrome"
once I want to update my profile, as that part of the website isn't compatible with "Firefox 3" yet.
For my normal browsing I stick to "Opera 11" quite stubbornly,
while this Vista came with an unused "Internet Explorer",
giving me a grand total a four browsers on one machine.
Now I am just hoping no "browser war" will erupt between them locally on this machine...