Searching using the exact word(s)

The Thunderbird search feature use some kind of fuzzy search, but I would like to be able to search for the exact word I typed. One example is if I look for "assurance", Thunderbird will show results for "assurer", "assurent" in addition to "assurance", but I would like only the email with the exact word "assurance" to be returned (sorry, my last search was using a French term, but you get the gist of my question even if you don't speak French). I tried putting the word between double quotes or adding a + sign in front of the word, it doesn't work. Any option I didn't see that would let me do this or is it a feature request I'm asking here? I didn't find anything in the documentation, nor any add-on that would be helpful. Even when I’m sorting the results by relevance, with the number of emails I have, it's not as helpful than finding the exact word(s) I'm searching, which is what I want most of the time.