No, that’s bookmark keywords, which are not widely used and difficult to discover, and for which there’s a rough alternative in search engines. I believe it’s on the chopping block, or at least it looked to be a few months ago, as I discovered when looking through Bugzilla to see about exposing bookmark keywords to WebExtensions so that I could make an extension that would implement DuckDuckGo’s !bangs in the browser.

Tags, on the other hand, are actually shown in the regular UI without needing to open the full bookmark manager. Much more discoverable, at least.

If they get rid of bookmark keywords, without some other equivalent mechanism (i.e. one that lets me set up URL bar commands so that "wp X" -> roughly "en.wikipedia.org/wiki/X", "g" -> "mail.google.com/u/0/h", and so on), then I will be really annoyed.

It’s possible to use search engines instead, but creating your own basically requires you to find or craft a search box that is equivalent to the desired action. It’s in no way easy to work with (not like making a bookmark with the %s placeholder), and isn’t quite as pleasant to use in the awesome bar either. I’m with you that removing bookmark keywords would be very annoying at present.

Note that it should be pretty easy to write an add-on that generates a search provider. It's just a simple (and open-standard) xml format.

Not enough time to write one myself these days, but if keywords disappear, I might.

To alleviate the pain somewhat, I switched a while ago to setting DuckDuckGo as my default browser, and simply using their bangs. Saves a lot of configuration when setting up a new browser, and all the expected ones (!w, !yt, !g, etc.) work.

s/browser/search engine/

Well, they did improvements around keywords lately - whenever I type my keywords now they are highlighted in the URL field