sometimes you found the search engine of website in browser drop-down list. to add you own website search in that drop-down search engine list. you need to use opensearch format.

OpenSearch is a collection of simple formats for the sharing of search results.

The OpenSearch description document format can be used to describe a search engine so that it can be used by search client applications.

The OpenSearch response elements can be used to extend existing syndication formats, such as RSS and Atom, with the extra metadata needed to return search results.

So the main question is how to implement this on your website.

It very easy to implement, here you go

Example:-

1. Create a opensearch.xml file and upload it to root directory.

<!--?xml version="1.0"?-->
    <opensearchdescription xmlns="http://a9.com/-/spec/opensearch/1.1/" xmlns:moz="http://www.mozilla.org/2006/browser/search/">
        <shortname>findnerd.com</shortname>
        <description>findnerd.com</description>
        <img height="16" width="16" type="image/x-icon">http://www.findnerd.com/favicon.ico
        <url type="text/html" method="get" template="http://findnerd.com/?s={searchTerms}">
        <moz:searchform>http://www.findnerd.com/</moz:searchform>
    </url></opensearchdescription>

2. Paste this below code in header file of website, set href path to your opensearch.xml file

<link rel="search" type="application/opensearchdescription+xml" href="/wp-content/opensearch.xml" title="findnerd.com">