Earlier quoted context omitted.
Saka keys on Firefox has been a suitable replacement for me.
Not me personally, but there will always be a vocal minority who will complain about having their workflow broken. Any replacement will be missing some critical feature. For a person affected by this, it is a painful experience having their entire workflow broken so they resort to dire warnings on forums such as this one ('Firefox is finished without '). In this case, I think Firefox made a good choice in modernising…
Here's an issue opened June 9 that hasn't been addressed by the Mozilla team and hasn't had any updates in a month: https://github.com/cmcaine/keyboard-api/issues/1
Here's the request for a better keyboard API (referenced in the above) that's been open for over 2 years with no end in sight: https://bugzilla.mozilla.org/show_bug.cgi?id=1215061
I'm sure the new FF is going to make some users happy, but as you said, having your workflow broken is quite painful, and the Mozilla team has known about this for years but still not made the upgrade path bearable.