Vlad The minimum ask is that the search keyword and URL to be bookmarked are exposed in the "Add this page to..." (add bookmark) dialog, perhaps initially hidden under a "More Options" or "Search Options" button that reveals these fields when clicked.
An alternative minimum ask is that a keyword field is added to the search engines add/edit dialog [Preferences > Search > Manage > +]. I suspect that's where people who have used these features before in other browsers are most likely to look for them.