Although you can specify an additional address in an address book, there seems to be no way to use this address when composing an email. If I create a contact called Bob with two addresses, email@example.com and additionally firstname.lastname@example.org, then the auto-complete in the address part of the compose window will always select the first address. I should be able to somehow indicate that I want to use the additional address instead of the first one. If this functionality does in fact already exist, then it needs to be a lot more intuitive. I've had a good look (and even read the help!), but can't find out how to do this. This may be related to Bug 110049, but I couldn't actually make sense of that one! Mozilla 1RC3.
*** This bug has been marked as a duplicate of 59148 ***