First, the people you are complaining to here are all volunteers; we didn't design the software or write the code, nor do we benefit in any way when people donate funds to the further development and support. Second, font selection in email (whether with Thunderbird or other email clients) is more complex than when creating a document with a wordprocessor. Many users prefer to write in plain text and use its font options (available at tools>settings from main menu) and others prefer to use HTML messaging (which allows bold, underscore, italics, etc.), and settings for that are at tools>Composition from main menu. My suggestion: - leave the HTML alone, as the default serves the sender and receiver best. - set your preference for Arial and 13 pt at tools>settings, and also click the Advanced tab. That allows additional settings, such as minimum font size. The top of that pane is a drop-down menu that probably shows either 'Latin' or 'Other Writing Systems. Setting BOTH is preferred because you may receive messages from people using other character sets. SO, to ensure consistency on your messages, I suggest ensuring that settings for 'latin' and 'other writing systems' match. Yes, it takes a few minutes, but once done, you never have to revisit it. To give an example, I attached images of my own setup (calibri and 14 pt). Following those steps, your composition window should always reflect your preference.