SUMMARY
Firefox has a feature where a keyword can be assigned to different search engines. Over in bug 340283 there's a lot of debate about search order, however, I think the user often knows what kind of thing they're searching for.

I think some of the need to "get result priority right" would be alleviated, and it would be generally useful, if the user could say something like "%w firefox" to prioritize open Firefox windows (i.e., open windows), and "%a firefox" to prioritize launching Firefox (i.e., app launchers).

The Firefox search settings, behavior, and default keywords could be used as an inspiration for a potential UI/UX for this.