eBay France have put a restriction on that no other country seems to have. All eBay sites have restrictions on harmful code (including javascript), but not harmful code is always allowed.

eBay France seem to restrict all as standard and you will have to contact your eBay support to request that basic javascript be allowed. It seems they can allow it on a seller by seller basis.

Here is an example of a customer that is using it successfully now http://www.ebay.fr/itm/121378440111

I don't know why eBay France do this when other eBay sites in Europe do not, but hopefully if you get in touch with them then they can remove the 'restriction'.