[throwawayonduck]

But not in Firefox Android, without a third party add-on

[nxtbl]

Well, not directly. When adding a keyword, I put it in the name of the bookmark in parentheses. Thus eg. https://news.ycombinator.com/newest is with the name "(hny) HN new" and keyword hny. When typing hny in the address field the bookmark comes up and I'll just tap it. You can also search only from the bookmarks.