new_recenter_for_KeySnail.js

key.setCaretKey('z', function(ev){
    var frame = document.commandDispatcher.focusedWindow
        || gBrowser.contentWindow;
    var selection = frame.getSelection();
    var range = frame.document.createRange();
    var elem = frame.document.createElement('span');
    range.setStart(selection.focusNode, selection.focusOffset);
    range.setEnd(selection.focusNode, selection.focusOffset);
    elem.innerHTML = "<I>";
    elem.setAttribute("style","background-color: green; zIndex: 1000; position:absolute;");

    range.insertNode(elem);

    var box = elem.getBoundingClientRect();

    frame.scrollTo(frame.pageXOffset + box.left - frame.innerWidth / 2,
                   frame.pageYOffset + box.top - frame.innerHeight / 2);

    setTimeout( function(elem){elem.parentNode.removeChild(elem)}, 1000,elem );
    range.detach();
}, "カーソルを中心に移動し、強調", false);

デバッグ用出力をはずしわすれていたために、firebugのない環境で正常動作しない問題を解決しました。