From /?s=keyword to /keyword.html in root directory

I need that my search results look like http://www.domenname/search-results-for-keyword.html.
WordPress is installed in root directory. I tried with tweaking plugins (Search Permalink and Nice Search), I tried with plugin Redirection to create redirection from http://www.domenname/?s=keyword to http://www.domenname/keyword.html (URL look like http://www.domenname/?/keyword.html), I tried to manually modify htaccess file and I can’t make it work.
Please somebody help me. Thank you.