uepselon

This plugin offers your blog visitors a <a href="http://www.foxload.com/firefox-download/" title="firefox download" rel="nofollow ugc">firefox download</a> button in different formats and colors on the sidebar.
Different banner formats and colors are included. The plugin use the wordpress locale settings for proper language versions of firefox.
You can place firefox buttons as widget and if your theme does not support widgets, you can place this <code><?php if(function_exists('get_foxload_button'))get_foxload_button(); ?></code> php code at the preferred position in your template.

Foxload Firefox Download

Offers your blog visitors a firefox download button in different formats and colors on the sidebar.

Jeff Waugh

Add OpenSearch discovery and querying to your WordPress site, based on the 
<a href="http://www.opensearch.org/Home" rel="nofollow ugc">OpenSearch</a> specification, version 1.1.
After activating the plugin, your WordPress site will expose a standardised 
search interface, accessible to OpenSearch clients such as the <a href="http://www.mozilla.com/firefox/search.html" rel="nofollow ugc">Firefox 
search bar</a>.

OpenSearch

Add OpenSearch discovery and querying to your WordPress site.

Foxload Firefox Download vs OpenSearch