Inbox Font Size

I have tried a number of times with the mobile apps to increase the font size of my inbox but there doesn’t seem to be an answer. Now, I have tried this app and it’s the same problem. I’m using Firefox but have no problems with font size when I go to the web mail but try and use the Gmail app and it’s too tiny to read. There just doesn’t seem to be an answer no matter what I try.

Trixie-woo about Go for Gmail - Email Client, v1.7