Comment 11 for bug 50213

Further research has revealed that, in any case, that use of %FC in a URI to represent ü is inappropriate. HTTP URIs are only defined when the percent-encodings represent US-ASCII characters. If they do not, it is not specified how they should be interpreted; however, modern specifications such as RFC 3987, Internationalized Resource Identifiers, dictate that they be interpreted as UTF-8. RFC 3986, defining URIs, also recommends that future URI schemes that allow for character sets beyond ASCII, use percent-encoded UTF-8.

Firefox, it turns out, is smart enough to treat both %FC by itself (which is not a valid UTF-8 encoding), and %C3%BC (the UTF-8 encoding of ü) the same (which is apparently what the W3C recommends). Konqueror, unfortunately, currently treats the latter even worse than the first; both are broken.