thanks for taking the time to answer me.

Yes, I red it was wise to set the date between 2012 and 2015 so I did so right away when I booted the.phone for the first time.

Perhaps it is but, why would sites like this one work while others dont? Moreover my other devices (I have an x61 under debian 9, a windows PC) can access any site without problem and I could try with an android 5 smartphone and a nokia 610 under obsolete windows phone version and it worked perfectly as well... I'm completely lost

Maybe proxy or dns things I dont know I'll keep invetigating though
I live in deep countryside so I can't acces any other wifi source right now, but I'll try!

EDIT: I tried using 3G and it's.exactly the same.
EDIT2: I found a commun point between all sites I can't access: There are https... I just can't access secure sites. This is something I probably could fix changing the browser's settings (like the TLS things)... As microB is based on mozilla, I tried the about:config thing but nothing was prompted... Developper mod won't intall so I can't use term and change .js files values manualy.