Well, this is strange ---- just now, I clicked on another email address in Chrome and it did open a new Thunderbird email with that address in the To: field!! OK, upon further investigation, I see that the email addresses taking me to Gmail are coded that way (behind the scenes!). Sorry, false alarm. I've never seen an email address before coded to take you to Gmail! (and not the email client you've specified) This is really underhanded!