I got the original code from the internet in 2010. The file said it had been compiled by Jacob Rus. Since then, I have been using many Emacs keybindings in many applications running in MacOS, especially those based on Cocoa. The functionality is very limited (or nil) on Applications not based on Cocoa, such as Firefox.
When I got a new Mac in 2019 (still Intel base), I had a lot of trubble installing my Default Keybindings dictionary. Not only did I chmod'd it to make it executable, I had to do something (I don't remember exactly what, sorry, other than having to restart my Mac with some security turned off, and turning it back on after installing the dictionary) to override MacOS's then new security features, apparently aimed at preventing users from fiddling with and potentially ruining their OS.
I might have had to create the new KeyBindings folder inside my home ~/Library/ directory, but, let me insist, that was the easy part.
I took advantage of the operation to add the ability to yank different segments of text (up to four) from the kill ring by hitting C-y repeatedly. I set this in the Terminal with defaults write -g NSTextKillRingSize -int 4 though it could be 8 or a different number.
According to Apple's "Cocoa Event Handling Guide", "If you set this to a value larger than one, you also need to rebind Control-Y to yankAndSelect: instead of yank: for things to work properly".
Not everything works as hoped for, but it does to a large extent. I like it so much that I've been tempted to move from Firefox to Safari only to be able to use my Emacs-like keybindings.
There's a lot of hype about Karabiner Elements now. I should give it a try.