Sharepoint : redirect to web homepage fails with access denied, on firefox onyl

Hi.

In SharePoint, accessing a web site using for example : https://a redirects to https://a/SitesPages/home.aspx (unless you did not change the home page).

Using IE or Chrome there ie no problem at all. Using Firefox: the redirection fails, and I get the famous "Sorry..." If in Firefox I try to access directly https://a/SitesPages/home.aspx it runs perfectly. So the problem is when using the mds and passing through _layouts/15/start.aspx# ...

Any idea for the right configuration in firefox? Or should i deactivate the MDS?