flash plugin with firefox and iceweasel

[Pierre Frenkiel]

hi,
I have some strange (for me) problems with the flash plugins
I have a laptop (amd64) and a desktop, both running debian wheezy
(multi-arch with i386 is enabled on the laptop)
On both, I installed the packages: flashplugin-nonfree (from debian)
and flash-plugin (from adobe)
I use the following link for the adobe flash player test:
http://www.chemgapedia.de/vsengine/help/en/flash/index.html

1/ on the laptop:
with firefox, it doesn't work at all
with iceweasel: works perfectly

2/ on the desktop:
until last saturday, it worked perfectly with both firefox and iceweasel
since yesterday,it works perfectly with firefox.
with iceweasel, it is half working, i.e. the spheres actually assemble,
but the movement is jerky, and there remains ghosts of the spheres
at their stating position.. very curious!

Has anybody an idea about how to explain there strange behaviours?

best regards,
--
Pierre Frenkiel