+1 to the improvement request. I have the same need. It would be very useful! Update: it would be also add an option to search in all users and in different users separately by shortcut and/or using a prefix (1: ... OR p: ...). Why: I have 2 user profiles - "private" and "work" one, and it is nice to do a search:
1) In all bookmarks → open in the corresponding user profile
2) In private only → open in the "private" user profile
3) In work only → open in the "work" user profile
Ideal option could be to select where the search is done by default and prefixes/shortcuts for each option (1-3).
Note: Chrome has a support for it (seen in other posts):
open -a "Google Chrome" --args --profile-directory="private"
OR
/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome {URL} --profile-directory={profile_ID}
Thank you!