User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:41.0) Gecko/20100101 Firefox/41.0 Build ID: 20150917150946 Steps to reproduce: Compose new email In body, set to Body Text, Fixed Width Enter a few lines of text. Then, for each line, apply a different, explicit, font size using the menu: Format | Size Actual results: Notice how the lines are displayed in the composition window, i.e. very little visual difference in the smaller sizes. Expected results: Each line of text should have been render accurately, in the correct size. After sending email and then viewing this sent email in the reader pane, the lines are visually correct; render is good.