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.
Except an already developed patch and proposal that needs some time from the main devs to be reviewed. For a long time they were very busy making FF bearable for 90% of the users. Now that it's released we'll see if this issue is as stuck as you imply.
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.