I mean, they also were developing usernames five years ago AFAIK. Adding usernames for everyone was the hard, but necessary step they finally managed to do. Only now is it possible to make accounts that are discoverable AND aren’t tethered to phone numbers. I’m assuming with passkeys/TOTP(?)

Try this: https://addons.mozilla.org/en-US/firefox/addon/ctrl-number-to-switch-tabs/

If it doesnt work, your best option is to either find another extension that does. or bite the bullet and configure a key remapper like keyd and make a “layer” to toggle the bind alt+(num) to ctrl+(num).