My expertise is derived from other users expertise! You will again have to go back into the Comcast preferences on the server to to Composing and select Plain Text instead of HTML. I'm pretty sure that's how it will work for you. Try that. Don't forget to save the changes as well.
Frankly I rarely use the webmail on my iPad other than to read and delete messages from the server. I have set my Xfinity mail up in the mail app. There are alternatives as well - the Xfinity mobile app for email. You can find it in the app store. The last one that I know of is to use the mobile website. Here it is.
http://m.comcast.net/i/#main_menu
Personally, I can't get the mobile site to work well either so I have stayed away from it. I'm sure there is something that I have overlooked on the mobile site but since I have other, better alternatives that suit my needs, I never cared about mastering the site!