Hi, I am running Mac OS 10.11 El Capitan, but this problem existed in 10.10 as well. Basically, I have the same issue as the two people before. When I go to preference, with each button I press, the window gets smaller and smaller until there is only one line. I am keyword this as "thunderbird preferences shrink." https://support.mozilla.org/en-US/questions/1084487 https://support.mozilla.org/en-US/questions/1080928 Disabling hardware acceleration does not work. Neither does removing add-ons. I am new to the forums and not technologically inclined. The same day I downloaded Thunderbird to my mac, I also downloaded it onto a Windows 10 machine. There are no problems within Options there.