With the invention of the opensearch specification, it has become super easy to create search plugins for Firefox 2.0+ and IE7. Here's an example:
<?xml version="1.0"?>
<OpenSearchDescription xmlns="http://a9.com/-/spec/opensearch/1.1/">
<ShortName></ShortName>
<Description></Description>
<Image height="16" width="16" type="image/x-icon"></Image>
<Url type="text/html" method="get" template=""/>
</OpenSearchDescription>
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