The link for Candy box 2 hard mode

Phew, finally finished it. WARNING! Huge spoilers ahead!

To open candy box you need to collect 4 marked stones: P,L,A,Y, as well as proceed to castle and defeat giant nougat monster to place this stones to tower.

After you place them on the tower, you will get talking candy, it's actually a key and end of the game - to get stones you need to (AFAIR):

Y

Y - defeat developer. You can take this quest from the dragon in the castle.

A:

A - defeat Devil in Hell. You can take this quest from the dragon in the castle.

L:

L - you can take this stone from the room in the castle with eggs. Use pogo stick and gravity potion, or unequip all of your weapons so you don't damage the eggs.

P:

P - from lighthouse puzzle, to get this quest you also need to talk with the dragon.

This sounds like an issue with a proxy, because candybox 2 does not use SSL at all (try searching for https in the source-code).

If your friend does not use a proxy, there's a small chance it could be due to browser plugins / anti-virus program / a virus / a national firewall / any number of other things. Have your friend post his issue to superuser.com (with many more details than you gave us here), since this is not a good place for troubleshooting connectivity issues.