The killer Firefox feature for me are multi-account containers. I haven't found another browser with that feature, and they make it SO much easier to deal with multiple accounts on the same site (Google, Facebook, AWS/GCP/Azure, etc.).
With Firefox, opening a new tab in a non default container has a terrible default shortcut, and you can’t remap it to anything sensible (like cmd + some letter).
I’m sticking with Firefox because I want to support them, but I miss Chrome dearly.
Just out of curiosity, have you tried creating a shortcut based on the menu name in the macOS global settings? As a Linux user who sometimes works for companies that issue Macs, that functionality goes a long way to preserving my sanity, but sometimes apps just hard-code a shortcut instead of using the OS.
(Extensions can do it, but they only take effect after the current tab is loaded.)