User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.0.4) Gecko/20060504 Firefox/1.5.0.4 Build Identifier: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.0.4) Gecko/20060504 Firefox/1.5.0.4 Thunderbird 1.5.0.4 on Linux (Mandriva 2006.1) freezes (application window does not update). This happens to me many times a day. I suspected it might be to do with large mailbox (I have several folders with thousands of mails, some contain more than 10,000); the number of folders (I just counted them and I have 96 folders under 'Local folders' alone); the number of accounts (two); or large emails. It's repeatable for me with a mail I'm currently preparing, which is fairly long (it's a Ubuntu security advisory, mirrored here: http://archives.neohapsis.com/archives/fulldisclosure/2006-07/0413.html to which I've added a few dozen more lines. I've had four or five crashes whilst trying to get this particular email sent (and yes, lost data in several of those events.) Reproducible: Sometimes Steps to Reproduce: 1. Use Thunderbird in normal way (for me) 2. ... 3. Actual Results: UI freezes, window(s) don't refresh, app never comes back and eventually I kill -9 it. Expected Results: App continues to run and respond. I'd be happy to do anything that might give you better diagnostics... it doesn't trigger Talkback though :(

This is the result of selecting the saved email in 'drafts' folder and doing 'View source' without actually opening the email. I just checked, and yes opening the mail in 'normal view' has killed Thunderbird again. The lockup seems unlikely to be *only* due to that particular mail content, presumably it's that plus other local configuration details(?)

Does turning off inline spell checking help? (bug 324521, fixed for 2.0)