Just found the JS error via JavaScript Console of Firefox:
Error: [Exception... "'Permission denied to get property XULElement.accessKey' when calling method: [nsIDOMXULLabelElement::accessKey]" nsresult: "0x8057001e (NS_ERROR_XPC_JS_THREW_STRING)" location: "JS frame ::
http://wiki.splitbrain.org/lib/exe/js.php?edit=0&write=0 :: anonymous :: line 436" data: no]
Source File:
http://wiki.splitbrain.org/lib/exe/js.php?edit=0&write=0
Line: 436
(IE and Opera show no errors or warnings.)