I don't know any easy way to search for font attributes. I've never encountered a situation like this.
Do you use Liberation Serif for anything in your document? For instance, for headings?
After you're done cleaning up this document, if you'd like to specify a default font for future documents -- for instance, Times New Roman -- there are good directions here:
http://www.pcworld.com/article/21423...ce-writer.html
Finally, do you use "Styles" for your documents?