I know this question has been asked and discussed at length, but creating a question appears to be the only way to create an account. If there is another way, please tell. To the question at hand, relying on an add-on for a simple configuration change such as modifying the UI font is really stretching things. I spent ages trolling through all the options in the default installation, and then went googling before I eventually found the add-on. I'm surprised it took so long to get the actual message across; perhaps it was ppl thinking differently, using different OSes, I don't know, but I recognized it straight away because it was exactly what I was trying to do. Change the font of the entire UI so that I could actually read it. The default is way too small for me. Changing the message text, etc., is simple; changing the entire UI is not. And again, don't want to change every app, only Thunderbird. I'm using Fedora 21. It might be worth considering that if so many ppl ask the same question, or have the same issue, then it might be worth making the "extension" part of the base functionality.