This is terrible news. I also have a keyboard-centric workflow and also make heavy use of keyword bookmarks. I too use custom bookmarklets containing JavaScript that I can invoke with a few key strokes for multiple uses including:

1: Auto-expanding all nested Reddit comments on posts with many comments on desktop.

2: Downloading videos from certain web sites.

3: Playing a play-by-forum online board game.

4: Helping expand and aid in downloading images from a certain host.

5: Sending X (Twitter) URLs in the browser bar to Nitter or TWStalker.

And all these without touching the mouse!

It’s really disappointing to read that Firefox could be taking so much capability in the browser away.