Vlad I know, but here is the concept: Every website that has a search input field which was placed into the history area which can be found by simply doing a search function with %s or whichever identifier search input fields use to input into the address bar, you simply make every single one of these queries be able to be automatically searched without having to go to the website first. For example, if you type "kagi, tab, then Orion browser", you will search for "Oriokn browser" on kagi. This is also available on Chrome and Firefox as well.
Please note that the right arrow with a line before it is the "tab" key in the video. Please pause at moments in the video if you still do not understand it.
Since this is on Firefox, you may look into taking some inspiration from the code of Firefox's search bar and how it auto completes websites.
Please note that this specific "auto adding" is not yet added. Yes, there exists the option to add custom search engines, but that is not the same as Safari just simply automatically adding all search input fields into the history to be navigated, or even adding input fields as an option to be bookmarked. None of these two options have yet been added.
I would appreciate the adding of two of these functions, but if not enough time then the latter would be appreciable for a while, but Safari's auto search feature is still a nice feature to have for more parity with Safari.