Typing a "c" in Gmail's Inbox does not open a Compose window

I'm using a MacMini (late 2012) with Sierra (version 10.12.2) and Safari (version 10.0.2 (12602.3.12.0.1))

This site, https://support.google.com/mail/answer/6594?co=GENIE.Platform=Desktop&hl=en
says that by simply typing the letter "c" from Gmail's Inbox, a compose window should open.
(I'm not referring to the app "Inbox by Gmail". Rather I'm accessing my Gmail Inbox by signing in with
my email address and password from the main Google search site.)

Not for me.

Instead, when I press the letter "c" while in my Gmail Inbox, I jump to the next tab in the same window.

I have enabled Gmail's "keyboard shortcuts," as well as the lab, "Custom keyboard shortcuts by Alan S"
both in Settings.

Some of the other keyboard shortcuts do work.

Holding down shift while clicking Compose opens a compose window.
Holding down shift while pressing "c" does the same thing.
The disadvantage of this window is that when I send the message, the window
doesn't close. I have to Cmd-W to close it.

In Gmail Settings > Keyboard shortcuts, the "Compose" is supposedly activated with "ç".

Goggle says "ç" is the letter "cedilla", used in latin, french and many other languages.

The combination of Alt-c produces a cedilla: ç

But typing Alt-c inside Gmails Inbox does not give me a compose window.

I've tried setting the lab to other keys, but each one, when I try to save my change,
produces a message, "One action per key!"

I've tried this action in FireFox ... and it works: typing a "c" from the Inbox of Gmail
does open a new Compose window. So its a Safari thing.

Does anyone have any thoughts?

Is the "Custom keyboard shortcuts by Alan S" working 100% for anyone?

Thanks!