[bmacho]

I don't have that. Where? Algolia and google search boxes(? the input fields?) don't show anything like that.

edit: also if I modify a keyword for my opensearch/xml search engines in about:preferences#search , it won't show up as a regular bookmark. Also I can't even see the URL for those search engines.

[velut]

Right click inside a search box. There should be the option "Add a Keyword for this search".

[bmacho]

Where? What is a search box?

[velut]

The search input provided by a website. You can try with the one in the footer of Hacker News and it works. See https://imgur.com/oxqMw6D