Here are a couple of things you can do. 1) If ''everything'' in Thunderbird is too small, I'd try changing a setting in the Config Editor. Go to '''Tools|Options|Advanced|General→Config Editor''' Tell it you will be careful. Type ''layout.css.dpi'' into the search box. What value does it have? The default is -1. If you want to make things bigger, change this, for starters, to 96 and see what happens. Try increasing it to 100 and decreasing it to 90 to see the effect and use trial and error to find a number that suits you. 2) If it's just the text in messages, go to '''Tools|Options|Display|Formatting→Advanced''' and set the sizes there. Do it for both ''Latin'' and ''Other Writing Systems''.