用markitup在firefox中出错

Question

使用MarkItUp Editor

时出现以下错误

 uncaught exception: [Exception... "Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIDOMNSHTMLTextAreaElement.selectionStart]"  nsresult: "0x80004005 (NS_ERROR_FAILURE)"  location: "JS frame :: /jquery.markitup.js :: get :: line 418"  data: no]

该行是

 caretPosition = textarea.selectionStart;

我搜索了互联网，但发现没有任何帮助我。问题出在firefox 3.6和4.1中。