From: Dmitry Gutov <dgutov@yandex.ru>
 Cc: Eli Zaretskii <eliz@gnu.org>,
         "56682@debbugs.gnu.org" <56682@debbugs.gnu.org>,
         "monnier@iro.umontreal.ca" <monnier@iro.umontreal.ca>
 Date: Fri, 12 Aug 2022 19:35:57 +0300
 
 I have eliminated two performance problems frim js-json-mode that are uncharacteristic for font-lock in
 general. One used a pathological matcher (simply removed), and another uses the "frameworks" facility
 which simply always rescans the full buffer from the beginning. That one can/should be fixed later, but I have
 disabled it for JSON (where it doesn't make sense anyway).
 
 You should know that the rest of js-mode's font-lock keywords are still there. I experimented with leaving just
 the bare minimum needed for JSON, but the effect was very minimal (like 20% improvement).

I didn't yet have time to try the branch, but what you say begs a
question: does the branch attempt to solve the problems of JSON files
only, or does it attempt to solve a more general problem?