Allow to enchance search on page option

Allow to use search engine description file to search on field accessible via ALT+K (search field). When page is loading, Firefox will check it’s a link to search engine description file, like Google, etc. and for JS file for extended search. User can type ALT+K, input terms and select one of: browser search engine (like Google), normal search method (available already by pressing CTRL+F), site search engine (normal mode - user must click enter to send request) and site dynamic (with auto complete for example) search method (controlled by loaded script).