Rated 5 out of 5 stars
Whatever I do (with p.e. all disabled except sender) using the quick filter box (enter) or the unified search box (ctrl-enter), the results are always the same. It returns matches from all folders with search term in sender, recipient, subject and body.
I tried to hide built in filter bar, but nothing changes.
My Thunderbird version is 52.5.0 (32-bit)
Can you try to disable this add-on, restart and check if the problem persists with the quick filter box?
(by having the same results with the standard box, It looks to me that the problem doesn't comes from the add-on, but by trying with it disabled we can be sure of it).
PS: you can email me if you prefer, better than adding more reviews: [email protected] but up to you.