When I try to import Wikidata or German Wikipedia search into Firefox, I get an error window:

Firefox Developer Edition could not install the search engine from: https://de.wikipedia.org/w/opensearch_desc.php

The Browser Console (Ctrl+Shift+J) reveals a slightly more informative error…

Invalid search plugin due to namespace not matching.

… from this code location: [nsSearchService.js, line 1809](https://dxr.mozilla.org/mozilla-central/rev/cec4a3cecc29ff97860198969b6fdff24b9e93bb/toolkit/components/search/nsSearchService.js#1760-1784).

It looks like Firefox only accepts the following namespaces (source):

const OPENSEARCH_NS_10  = "http://a9.com/-/spec/opensearch/1.0/";
const OPENSEARCH_NS_11  = "http://a9.com/-/spec/opensearch/1.1/";

// Although the specification at http://opensearch.a9.com/spec/1.1/description/
// gives the namespace names defined above, many existing OpenSearch engines
// are using the following versions.  We therefore allow either.
const OPENSEARCH_NAMESPACES = [
  OPENSEARCH_NS_11, OPENSEARCH_NS_10,
  "http://a9.com/-/spec/opensearchdescription/1.1/",
  "http://a9.com/-/spec/opensearchdescription/1.0/"
];

In I2c261cd654, we switched from what Firefox calls OPENSEARCH_NS_11 to a custom namespace, http://www.opensearch.org/Specifications/OpenSearch/1.1, which is not recognized by Firefox, which is why the search engine no longer works.

Is that new namespace part of any specification? (The version linked from that namespace URL itself still uses the original namespace.) If yes, I suppose we should file a bug in Mozilla’s Bugzilla to get it added to their list, otherwise we should revert our change.