Sorting products Firefox/IE

Dears,
I have a real strange issue….
On page https://regence.be/categorie-produit/catalogue-du-19-novembre-2016/
The order of products are all right, except on Internet explorer and Firefox….this is really strange as on my mac Chrome and Safari are displaying products in the right order.

See screenshot: https://i.imgur.com/Ecfh5Ma.png

I cleared cache and purge cache on server but still same issue for some browser….
Can you pls help me or tell me where to search?
Thx
Pierre