User:Beltzner/How to Make GMail Not Suck for Bugmail
From MozillaWiki
Include the following in your userContent.css file (in your profile):
div.msg div.mb { font-family: monospace !important; font-size: 12px !important; } textarea.tb { font-family: monospace !important; font-size: 12px !important; } td.ct { font-family: monospace !important; font-size: 12px !important; }