Or add "w" keyword for https://en.m.wikipedia.org/wiki/Special:Search?search=%s&go=... bookmark on Android Firefox and then search with "w searchstring" from its address bar.

It's silly that it's necessary to create separate bookmark for this, though. Native search engines, surprisingly, don't support keywords there.

Why silly? It is in fact a bookmark - just a parametrized one. :)

They do have native search engines with neat option to add them from a site's search field. Why not add keywords too as they did on desktop.

I feel silly adding bookmarks for the things I already have in search engine list.