Bind the Ctrl + <number> keys to firefox in Ubuntu

On Ubuntu Ctrl + Number doesn't work. Instead you have to use Alt + Number

Both Alt keys work. This works on Chrome and Firefox and File Manager... essentially anything with tabs open.

It works in Unity, GNOME and Cinnamon (as you wanted).

How am I supposed to close tabs
-– HackToHell

You can close tabs with Ctrl+W. This also works on windows and Mac (Cmd+W)

I suppose there is no way to restore it back to good old Ctrl+ ? – HackToHell

Alt + Number is just as easy as Ctrl + Number (just a matter of getting used to it). I think that Ctrl + Number may be used for other ubuntu things?

The amount you would gain from rebinding it is nowhere near the effort you would put in to change a system wide shortcut key.

The Firefox Add-on Addressable-Tabs let's you do exactly what you requested. Basically sets the hot-key to Ctrl+1–9 while also maintaining the Alt shortcuts. Works with Ubuntu 18.04 on Firefox Quantum.