The non-standard, Netscape-derived
window.sidebar object, an alias of
window.external, is now officially considered deprecated and will be removed in the future. The object is no longer available on the Nightly channel as of Firefox 65. Web developers must stop using it for browser detection.
window.external object will remain, but the
IsSearchProviderInstalled methods on it will be no-op, simply returning
undefined, according to the latest HTML spec. This change has also been made to Firefox 65 Nightly. While
AddSearchProvider could be used to add an OpenSearch plug-in to the browser,
IsSearchProviderInstalled was always returning
0 on Firefox.
There is no plan to remove the auto-discovery of search plug-ins via
<link rel="search">, which is a recommended way to provide an OpenSearch plug-in on a website.