I've been using Thunderbird for about two months now and I just realized that Thunderbird (150.0.1) seems to be unable (or unwilling) to use some of the fonts that are on the computer (Windows 10, plenty of RAM and disk space). Let me explain that I don't send a lot of emails, and most of the ones I do send are just a few lines so I had not had any reason to bother with the font -- the default font was fine -- until today... Today my experience with fonts in Thunderbird was extremely disappointing. It started when I was composing an email and I copied/pasted some text from a web page into the email. Rather than treating the pasted text as simply text to have in the default font, Thunderbird put it in some strange font and size. This might have been Thunderbird's attempt to use the font from the website but neither the font nor the size resembled the text that I had copied/pasted. That was when I noticed that Thunderbird does not let you choose the actual size but only offers the choice to make text larger or smaller. Making the text smaller was sufficient for that particular time. As I finished the email, I tried to sign my usual signature. Thunderbird lets you choose the font but once I had chosen the font that I routinely use for my signature, I discovered that Thunderbird totally ignores the choice that it just let you make. Instead of displaying the signature in the chosen font, it displayed my signature in a plain sanserif font. I could live with a limited choice of fonts -- I have used another program where the only choices were serif and sanserif -- but I cannot understand why Thunderbird would offer a font choice menu that includes all my installed fonts when it actually only honors three choices. The only fonts reliably used seem to be some generic sanserif font that Tunderbird calls Helvetica/Ariel, a generic serif font that it calls Times and another serif font it calls Courier. The dropdown menu lets me choose any of the fonts I have installed, '''some''' of them display properly while composing the email, others don't. If I send the email to another of my email addresses, Thunderbird displays the text the same way -- some fonts are correct and some fonts get replaced with one of Thunderbird's generic fonts. I'd really like to have all my fonts available -- but that doesn't seem to be possible with Thunderbird so I guess I need to figure out which fonts Thunderbird is willing to use.