How to make F4 --or another function key or keystroke combination-- open/close Calculator?

[JohnDohe]

Hi!


I tried using Automator to program F4 to launch Calculator.


But it works erratically:
F4 works to launch Calculator in:
Preview
Calendar
Dictionary
Safari
Photos
Microsoft Word for Mac 2016
Microsoft Excel for Mac 2016


In some of the above apps tapping F4 as soon as I opened the app did not work the first time
to launch Calculator.
I had to first mouseclick my "Launch Calculator F4" service, Calculator would launch,
then I'd quit it, and then F4 worked to launch Calculator by just pressing F4.


However . . . F4 does NOT work to launch Calculator in these apps:
CONTACTS
TEXTEDIT
MESSAGES
I get a "bonk" sound when I press F4.
My created "Launch Calculator F4" is under Services and when I mouseclick it Calculator launches.


F4 also does NOT work to launch calculator in FIREFOX (v83.0)(64-bit):
. . . But this is different:
When I press F4 the FireFox name in the FF menu bar flashes white letters on a blue rectangular background
and does NOT launch Calculator.
However, my created "Launch Calculator F4" is listed under Services and when I mouseclick it Calculator launches.


I use FireFox as my browser.


I would like to know how make F4 --or another function key or keystroke combination--
work in Firefox as well as in ALL Mac apps to open and close Calculator.


Please advise!
Thanks!