Well, I may have found a way to bypass the browser protection, you have ninjhax 1.x installed on your CN cartridge ? If so what you could do is get yourself a copy of pastacfw (easiest way to get sig check disabled without firmlaunch...) and a copy of devmenu or big blue menu, either should be fine.
Then you fresh boot your 3ds, launch ninjhax, launch pastacfw, you'll end up in home menu again, launch ninjhax again and then launch fbi, from there install your copy of BBM or devmenu.
Then reboot your 3ds, go to ninjhax, boot pastacfw, launch BBM or devmenu, look through the app list for "browser" launch it, and it should bypass the parental lock.
Then simply go to gateway launcher website to launch gateway, and then downgrade your 3ds to 4.x, this should finally wipe the parental control.
This is the easiest method I could come up with.
I don't guarantee that it will work (mainly the launch of browser, should work, but can't check right now...) But I am sure that a downgrade would wipe the parental control for good.
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He has a O3DS, this won't work.