Even just composing a simple HTMl, it's buggy on my end. The blockquote quotes the entire text box rather than what you highlight and when you create a link, it links the entire text box. I don't know if this is only on mac or just firefox. Any other program when you email a webpage, gets converted to link, seems like I only have this issue with Roundcube. On iphone and ipad, roundcube is pretty much unusable.
It also doesn't explain why
<!-- html ignored --><!-- head ignored --><!-- meta ignored --><body><p></p></body>
Gets added to the compose window anytime I try to email a webpage.