Can't reach Google running browser in a sandbox


I am moving my first steps with Comodo, and I found a problem with sandbox; I had a look in the forum, but I could not identify a solution to my problem… maybe it is due to my low experience.

Well, my problem is: every time I run a browser (normally Firefox) in a sandbox, I can no longer reach Google - and it looks like other https sites too; the error code I get is SEC_ERROR_UNKNOWN_ISSUER.
Apparently it has to do with certificates, but I get no issue if I run Firefox in the normal way.
(For information, I’m using Windows 10 and CFW latest edition, and firefox too).

Anyone found the same issue? Or has any idea to fix it?
Or… where am I wrong?
Thanks in advance to anyone can help me.