Main window font too small to read with impaired vision

I am using Thunderbird 60.5.3 on a MAC. The font size of the lists of emails on the main screen is so small that both my wife and I have great difficulty reading it. I know how to increase the font size of individual emails, so it's just the main window which is such a difficult problem. I have tried to down load a font size add on but this does not seem to work. This is a major downside in using Thunderbird. I'm not a natural computer person so a simple solution please!