Thunderbird 60.5.3 Font Is Too Small on Apple MacBook

[artmanphoto]

I am using Thunderbird 60.5.3 on a Macbook Pro (Mac OS Mojave 10.14.1) laptop. In an attempt to increase the screen font size using the Configuration File preference "layout.css.devPixelsPerPx" I entered a number value too large and the screen font increased so much that I am no longer to see the "Config Editor" button in Options-General-Advanced to open the Config Editor to change the preference to a smaller number to make the screen font smaller.

I am hoping to locate the Configuration File in Thunderbird in the Macbook "Finder" and make a manual change in the preference to a smaller number to reduce the screen font size.

Can some please tell me where the Configuration File is located in Thunderbird 60.5.3 in Mac OS so I can attempt to make the change? Is there any other way to fix this issue?

If not, the only solution I know is to re-install Thunderbird onto my Macbook Pro.

Thanks very much for your help.

Bill