http://tech.cybernetnews.com/2007/04/24/cybernotes-my-top-10-thunderbird-2-extensions/
Now that Mozilla’s Thunderbird 2 is finally released there will probably be a lot of newcomers trying out this top-notch email client. A lot of people don’t realize that Thunderbird actually has extensions that you can install much like Firefox, and so I thought I would point out some of the best Thunderbird 2 compatible extensions that are available
i like this one…i use also for my yahoo and gmail email…beside my regular pop3 account through my isp 
Webmail
Not all email services, such as Hotmail and Yahoo!, offer the POP access which is necessary to download/send your emails. Believe it or not there is an extension that will help get around that problem and it is called Webmail. With this you’ll actually need to install at least two extensions, one which is the main Webmail extension and then you’ll install an extension for each of the email services you want Thunderbird to work with. For links to all of the add-on components as well as installation instructions just see this page
http://webmail.mozdev.org/domains.html
One of the most precise articles on T’bird extensions up to date. It should be noted that Lightning didn’t break when updating to T’bird 2.0. I say this because the old calendar broke up when updating Firefox to FF2. Thanx for the post.
i really like thunderbird especially the new 2.0 verison-don’t use outlook express,eudora or others AT ALL 8)
I really like Thunderbird 2. IMHO it’s much better than OE. And lightyears ahead of Winmail (Vista’s sucky email program)
As for Add-ons (extensions), I use “Buttons!”, “Quote Colors” and “Contacts add BCC Button”
I know this thread is about Thunderbird 2 extensions, but I’m not totally off-topic as you mentioned not all email services, such as Hotmail and Yahoo!, offer the POP access which is necessary to download/send your emails.
eprompter can download/send your webmail, such as Hotmail and Yahoo!, as well as alert you of new emails. I like Thunderbird, but I find eprompter to be more convenient. However, it only does plain text.
http://www.eprompter.com/
Well thunderbird can d/l your hotmail and yahoo emails using extensions.
I use Signature Switch, Folderpane Tools to organize my accounts & signatures. I tried many e-mail apps but Tbird works best for me.
Ok, I tried webmail, works perfectly, good buy Yahoo POPs!
Thank you drhayden1