Is the problem related the FR Tree Viewer by Cynwoody or the “Greasemonkey” extension that allows it to work? (JS?). If Greasemonkey related, then there is a Brave extension that does the same thing called “Tampermonkey”.
https://chrome.google.com/webstore/search/tampermonkey “Brave” is based off of Chrome (w/o the spy stuff obviously) thus the Chrome extension store.
After the newer (post 47?!) FF update, cynwoody integrated his add-on to be able to install directly to FF, without greasemonkey/tampermonkey ( had both installed). I remember having issues after the update, and he explained it to me, at the time.
Brave, if I remember correctly, has steps to install Chrome add-ons, which I followed, but it still isn’t showing up :/
I may look into it again later.
(Oh, P.S. I don’t think it would be a FRTree viewer issue, unless it has something to do with permissions..)