Icecat vs. iceweasel

[Andreas Enge]

Hello,

there are a number of sites for which I still need to use iceweasel, since
icecat will not work on them. Now it may well be that the site is also poorly
configured, but it is still surprising that the two behave differently, and
I wonder whether there is something to be done in our icecat setup.

For instance, if I try the following site:
   http://www.francevivipares.fr/siteafv/
enter an arbitrary (right or wrong) password and click on submit,
the following error message is displayed:
IceCat has detected that the server is redirecting the request for this address 
in a way that will never complete.
This problem can sometimes be caused by disabling or refusing to accept cookies.

Even when accepting third party cookies, the site does not work.

Does anyone have an idea what is happening?

Andreas