Add an OpenSearch file: https://developer.mozilla.org/en-US/docs/Web/OpenSearch ...

Add an OpenSearch file: https://developer.mozilla.org/en-US/docs/Web/OpenSearch

Maybe something like:

  <OpenSearchDescription xmlns="http://a9.com/-/spec/opensearch/1.1/"
                         xmlns:moz="http://www.mozilla.org/2006/browser/search/">
    <ShortName>Marginalia</ShortName>
    <Description>Marginalia Search - a search engine that favors text-heavy sites and punishes modern web design</Description>
    <InputEncoding>UTF-8</InputEncoding>
    <Image width="16" height="16" type="image/x-icon">https://search.marginalia.nu/favicon.ico</Image>
    <Url type="text/html" template="https://search.marginalia.nu/search?query={searchTerms}" />
    <moz:SearchForm>https://search.marginalia.nu/</moz:SearchForm>
  </OpenSearchDescription>

and then add:

  <link rel="search"
      type="application/opensearchdescription+xml"
      title="Marginalia"
      href="/opensearch.xml" />

to your page's <head>.