Firefox supports OpenSearch, you can just go to any search engine (like my searxng site) and right-click the address bar to add it to your search engines.
Or you can manually add it from settings by just adding the address of the search site.
It will determine the proper format automatically, no need to add the %s stuff you typically would.
Firefox also handles suggestions properly, Chrome doesn’t seem to support them at all outside of their engine.
Why do you need a hack?
Firefox supports OpenSearch, you can just go to any search engine (like my searxng site) and right-click the address bar to add it to your search engines.
Or you can manually add it from settings by just adding the address of the search site. It will determine the proper format automatically, no need to add the
%sstuff you typically would.Firefox also handles suggestions properly, Chrome doesn’t seem to support them at all outside of their engine.
At least for me, to manually add the search engine, I had to follow this superuser answer to be able to add the custom search engine.
Maybe the search engine you were trying to add doesn’t support OpenSearch?