>> Firefox Setup <<
Mozilla Firefox maintains an internal whitelist of top-level domains (TLDs; e.g. .org or .uk) whose registries have appropriate anti-spoofing policies, to make sure two different people cannot register names which are confusingly similar to the eye. IDN domains whose TLDs are not on the whitelist display as "xn--something" (a.k.a. A-labels or Punycode) in the UI. This approach means an IDN URL either works in Firefox everywhere, or nowhere - it is not dependent on the settings of each user's computer.
The 11 example.test TLDs are whitelisted in Firefox 3 and above, and so no further configuration is required. Work is under way to ascertain the anti-spoofing policies of the registries responsible for the new IDN TLDs, and then whitelist those as well. Mozilla actively recommends against ordinary end-users adding TLDs to the whitelist manually.
