Do you miss gmail sound notification in Thunderbird?
Thunderbird is able to notify you by playing a sound whenever new mail arrives for any of your accounts, even a gmail pop3 account.
However sometimes gmail sound notification may not work, although all normal pop3 accounts still announce new mail with a sound.
To solve this problem, just empty your gmail inbox (select all messages and delete or move them). It seems that after a while, when a certain number of messages is gathered in the inbox of gmail, sound notification faces a problem.
Another solution would be to install Mailbox Alert, a Thunderbird addon that will put a context-menu option in all Thunderbird folders, letting you activate sound notification for any of them. Unzip the archive anywhere you like, and from inside Thunderbird Addons install the .xpi file
You can also use this free Gmail Desktop Gadget, that will check for new messages on your gmail account independently from Thunderbird.