http://www.mozillamessaging.com/en-US/t … extensions

# If you use or had previously used the master password feature, you may be prompted to enter your master password when you first start up Thunderbird. (Bug 338549)

# Your passwords are stored in a new location. If you go back to using a previous version of Thunderbird, or switch back and forth between Thunderbird 3 and an older version, your password lists do not get updated.

# Searching your emails is case sensitive for languages other than English. (Bug 525537)

# If using SSL or TLS, and the certificate that comes from the server is self-signed, expired, or has a domain that does not match the server domain, a dialog will be shown asking if Thunderbird should permanently make an exception for the cert. This should only be done if the error is understood.

# The extended columns in the folder pane were removed in Beta 1. There is an add-on that restores this functionality. - https://addons.mozilla.org/en-US/thunderbird/addon/9716

# The compact header view was removed in Beta 3 (Bug 480623); see this blog entry for details.

# Some Thunderbird 2 users upgrading to Thunderbird 3 may not be able to login to their smtp server because the secure authentication setting maybe turned on but not supported by the smtp server. Check your smtp server settings in Tools -> Account Settings -> Outgoing Server, and edit the smtp server with the issue. If use 'secure authentication' is checked, uncheck it and try again. (Bug 522633)

# Thunderbird requires that extensions either come from a secure server using the HTTPS protocol or are digitally signed, or they will fail to install.

# If you are unable to view content for your RSS feeds in the Wide View Layout, you may need to disable the Lightning Calendar add-on if you have it installed or switch to Classic View and restart Thunderbird. (Bug 531397)

# Some emails sent in Plain Text may move the message and some of the buttons out of the message pane. Open the message in a New Tab, resize the window, or change your layout to Classic View or Wide View to view the message. (Bug 530047)

# When working Offline, if you compose an email and select 'Send Later', your message may not be sent if you reconnect automatically to the Internet. You will need need to manually resend the email from your Drafts folder. (Bug 531179)

# In some cases, using 'Save As Template' from the File menu may not work. You can still Save As Template from the email Compose window or drag the message into the Template folder. (Bug 532050)