[ezekg]

Works fine for me in latest Firefox. I've never had it not work in a specific app. Though, sometimes the keyboard crashes and doesn't come back up until a restart (that could be the fault of my Ryzen Hackintosh, though).

[jfk13]

What exactly works in Firefox -- is it Command-Control-Space or just Command-Space?

[ezekg]

Cmd + space brings up spotlight, as it always has. Cmd + ctrl + space brings up the emoji keyboard.

Perhaps you have some forgotten keybindings, because that's the case on every macOS device I own.