User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN; rv:1.9.2.8) Gecko/20100722 Firefox/3.6.8 Build Identifier: 3.1.3 Beta I think there is a problem in the beta version of Thunderbird 3.1.3 we use a HTML file as our signature, in the file, we define the fonts should be Calibri, but when we compose Email, the fonts in the signature was turned into another fonts, such as the system default fonts, but the body of the Email can use the user-defined fonts, like Calibri Reproducible: Always