Since we have the new w3c notification you can click on it if you receive a new mail and the new email will open. I have set in the TB preferences to open new mails in a new tab, but the mail than always opens in a new window. STR: 1. Set Thunderbird to open emails in a new tab 2. Get one new email (if you get more than one, than the STR will not work) 3. Click on the notification that pops up in the corner --> The email opens in a new window, but should open in a tab Same issue should be in Seamonkey, but haven't tested this. I found this issue while testing the patch for Bug 852648.