OpenSearch appears to be a standards initiative from 2011. They claim that it is supported by IE, Firefox, and Chrome:
MDN implements the standard, and includes the link in the header:
<link rel="search" type="application/opensearchdescription+xml" href="https://developer.mozilla.org/en-US/search/xml" title="Mozilla Developer Network">
If you use the separate Search toolbar in Firefox Quantum, you can still add MDN as a custom search provider:
You don’t get it with the default omnibar, however.
We also refer to
rel="search" on the reference page, and point to this documentation.
I think we should move the page out of AddOns (maybe as a top-level page), and start making it a generic document for the OpenSearch standard. It seems like a useful open web technology that didn’t quite make it, but still could be incredibly useful for sites like developer.mozilla.org, stackoverflow.com, and intranet sites.