If you're looking for a more Gmail-like experience in Thunderbird 3.3 alpha, a new add-on should be able to help you out.
Dubbed Thunderbird Conversations, the add-on offers a conversation view in the e-mail program, allowing users to have all their messages to and from another party in one place, similar to Gmail. The app "fetches" e-mails across every folder in the user's Thunderbird installation. Users can reply to an e-mail inline, and access the add-on's "contacts auto-complete" feature to streamline its use.
Thunderbird Conversations was first made available at the end of last week, but it was formally announced on the Mozilla Labs blog earlier today.
If Thunderbird Conversations sounds familiar to current users of older versions of Thunderbird, there's a reason for that. The add-on is a totally rewritten version of the former Gmail Conversation View, available to those using Thunderbird 3.1. The add-on's developer, Jonathan Protzenko, claims Thunderbird Conversations is "a significant improvement over previous versions." However, he also noted on the Mozilla Labs blog that the new Thunderbird Conversations will only work with Thunderbird 3.3 because it includes "the required support" for the add-on.
Thunderbird 3.3 alpha was released at the end of November and includes support for Windows, Mac, and Linux. Along with its launch, Mozilla announced that the e-mail program would not support PowerPC-based Macs going forward.