This version fixes a lot of annoying small bugs. The most important change in this version is the switch to GitHub to open up the development process. There are now links to the bug tracker and the wiki. Here's the full Changelog.

GMail Conversation View 0.3beta2
--------------------------------

- Various bugfixes from Justin Hileman: Makefile fixes, monospaced text
wrapping...
- Visual refresh of the conversation view, many thanks to Justin Hileman.
- Fix the Makefile to be compatible with older versions of zip.
- Be compatible to some degree with options mail.correct_threading and
mail.strict_threading (the "open in new tab" feature won't work though).
- Add an option to display message snippets using a monospaced font.
- Fix issues with the options dialog size on Mac.
- Display proper icons in the "Customize palette" dialogs.
- There is now an indication for messages that are drafts.

GMail Conversation View 0.3beta1
--------------------------------
- Fix packaging bug. All development builds between 03/01 and 03/07 won't work.
- Fix the visual appearance of the button in the mail header toolbar.
- Fix a bug where error messages would remain stuck on the screen.
- Added an option (disabled by default) to mark the whole thread as read when
the conversation view is loaded.
- The extension now uses a jar file for better performance.
- Revamped options dialog (much better).
- The extension's icon is now visible in Thunderbird 3.0.x (only in 3.1 before)

GMail Conversation View 0.3alpha3
---------------------------------
- Make the extension still work when the "Global search and indexer" is
disabled. You won't get all the features but it should improve your experience
anyway.
- Added more meaningful error messages.
- Warn people when "Global search and indexer" is disabled (this prevents the
extension from working).

GMail Conversation View 0.3alpha2
---------------------------------
- Conversations are now automatically pulled by default (this can be disabled in
the options dialog). This means that if you reply to someone's message, although
there is no thread in your inbox, the conversation view will appear whenever you
select that message. This adds some extra stress on Thunderbird so this can be
disabled in the add-on's options.
- Added links to reply (and other actions) to an email in the conversation
directly (it's not necessary to open the message first anymore). You can hold
shift while clicking the links, it will work as expected.
- Added support for viewing messages as HTML (now enabled by default). Many
rounds of improvement. This should be perfectly usable now modulo bug 540911.
- Added folding support for HTML emails, added some heuristics to detect more
types of quotes than Thunderbird does by default (Hotmail-style,
Outlook-style, "----- Original message -----"-style...). Please report any false
positives.
- Many improvements to the way HTML messages are displayed: JS, displaying
images now follow the global content policy, inline images are properly
displayed, HTML is sanitized, and many more...
- Added a small button that allows you to toggle between monospaced and regular
font for viewing plain/text messages. Useful for Bugzilla emails for instance.
- Added an option to reverse the order of messages (last -> first)
- Fixes a bug where a thread would be incorrectly summarized as more than one
conversation. This is actually a bug in Thunderbird, see bug 538750.
- Fixed a bug that would render tab characters incorrectly in plain/text
messages with fixed-width fonts.
- Fixed a nasty bug where dates were displayed using a wrong character set.
- "Mark all read" now also marks your own messages as read. The menuitem was
sometimes incorrectly grayed out. This is now fixed.
- Improve the look of printed messages (many more improvements).

This is a preview release. Please do report bugs by email, not in the comments. I will need to contact you to get more information so leaving a comment is useless. Please check my to do list before reporting a lack of feature / a bug, it might already be there.

There's been a lot of under-the-hood improvements since the last version, plus a lot of new nice features based on user requests. See the Changelog below. I have a few more items left on my to do list, but I need to get a wider testing before releasing a 0.3 version. So please make sure you report bugsby email. Thanks !

Changelog:
- Rough HTML message support (slight improvements)
- Added a small paperclip icon next to messages that have "real" attachments (a
"false" attachment is an attachment you can display in the conversation view
such as texts, forwarded emails, old emails, etc.)
- Added a context-menu to the multi message view, that allows you to *print*
conversations. There's an associated "print style". Other various actions are
available through the context menu.
- Added extra buttons (+ preferences) when viewing a conversation : unfold all,
fold all, mark all read, open in new tab. There buttons only appear if viewing a
conversation, not a summary of messages scattered accross different threads.
- Added an option that allows you to focus the first unread message when viewing
a conversation (if all messages are read, focuses to the last message). This
should be working perfectly now.
- Fixed a bug when the add-on failed to retrieve certain messages and displays
"..." instead of the message's text.
- Fix some performance issues (optimize array accesses, remove jQuery animations
as it would considerably slow down unfolding of long emails).
- For GMail accounts, since the same message is in multiple folders, useless
changes of folders were performed when trying to display a specific message by
clicking on the sender's name. This is now fixed.
- For GMail accounts, clicking on a message *you* had sent would take you to the
"Archives" folder. This is now fixed and sends you to the "Sent" folder.
- Fixed some inconsistencies for GMail, such as: in the folder corresponding to
a label, the thread would select the messages in "Archives" instead of the
messages in the current folder, thus sometimes creating inconsistencies
regarding the read/unread status.
- Localized (only en-US for now)