I found a solution for filtering posts using QueryString, but I can't set UrlEvaluationMode to "QueryString". When I set this field to "QueryString" and save changes, then it automatically sets back this field to "UrlPath". I tried to set it even in blank page, but also nothing had changed.
Link to solution for filtering posts I found: http://www.sitefinity.com/blogs/slavo-ingilizovs-blog/2011/12/12/url_filtering_in_built-in_content_widgets
Thanks in advance,