The website is trying to add a search engine using a severely dated method that was dropped in Firefox 44. See Adding search engines from web pages for more information.

Unfortunately, if you are not the website owner or administrator, there is nothing you can do about this issue.

It used to work until the last update????

Firefox supports Sherlock but won't install the ad on

To the best of my knowledge, Sherlock plugins were dropped in Firefox 44 in favour of OpenSearch plugins, which have been around nearly as long as Sherlock plugins.

Unfortunately, the developer of that website is using a Sherlock version, not OpenSearch. You'll have to reach out to the website administrator to have them update that feature.

Sorry.

gregroovy2 said

Firefox supports Sherlock but won't install the ad on

Sadly it does not.

"Stop supporting installation of Sherlock plugins from the web. Search provider add-ons should be implemented using OpenSearch." According to Add-on Compatibility for Firefox 44 (Dec 29, 2015).

You can also refer to bug 862148 for more information.