Different top-level domains have different rules about what characters they'll allow in domain names. If a registrar has policies that prevent homograph registration, Firefox (and other browser vendors) will add them to the default whitelist.
If the .cn registrar has a policy that says "only ASCII and CJK characters will be allowed in domain names", then it's pretty unlikely that a homoglyph attack will work, and browsers will show the properly-decoded string as the domain name.
(and sure enough, my copy of Firefox sets "network.IDN.whitelist.cn" to true)
If the .cn registrar has a policy that says "only ASCII and CJK characters will be allowed in domain names", then it's pretty unlikely that a homoglyph attack will work, and browsers will show the properly-decoded string as the domain name.
(and sure enough, my copy of Firefox sets "network.IDN.whitelist.cn" to true)