Mozilla Foundation products now only display IDNs in a whitelist of TLDs, which have policies stating what characters are permitted, and procedures for making sure that no homographic domains are registered to two different entities. This work was done in bug 286534 by Jungshik Shin – thanks to him. I’ve made a list of the whitelisted TLDs with links to their registries and the relevant published policy documents. Our whitelist is currently (almost; see below) identical to that of Opera; I’d also like to thank Yngve Pettersen of Opera for saving me a lot of work in gathering this data.
(Note: .museum and .hu have been approved but we have not yet checked in the change to enable them. This is bug 299927.)