If you close, shut down or exit Thunderbird (or Thunderbird stops on its own) and you see the Thunderbird process is still running (in MS-Windows task manager aka taskmgr, or linux ps process status) then you have a shutdown hang. When starthing Thunderbird you may see an error message "Thunderbird is already running". Check taskmgr or ps to see whether thunderbird is there. If you don't see thunderbird listed then you do not have a hang.
What to do: 1. Go through the full symptoms list below. 2. If a Reported Bug is an exact match then cc yourself on the bug, but please only comment if you have new data to add. 3. If no bugs match, then report a new one, and provide detailed symptom information. In summary, just commenting that you see a hang is not useful - please support your report with symptom data.
To be most helpful, you will want to
- not be using an old version - please use the latest release, or better yet Early Bird or development (do a backup first)
- describe your environment (including anything which helps you avoid the problem)
- experminent to determine steps to reproduce, the complete sequence of steps before shut down needed to reproduce
- obtain a hang stacktrace
- Does Thunderbird hang ... :
- when Windows is started in safe mode? If it doesn't hang in safe mode then something running in Windows is interfering, like antivirus or firewall software. see firewall or antivirus software
- when Thunderbird is started in safe mode? If it doesn't hang in safe mode then disable add-ons until you find which add-on is causing the problem, then contact the add-on author.
- happen without calendar/lightning extension? (bug 532435)
- happen without enigmail extension?
- Is gloda indexing enabled or disabled? (Tools|Options|Advanced|General)
- What type of mail accounts do you have - pop, imap, or a combination?
- Did the computer go into sleep or hibernate while Thunderbird was running?
- Did you change Thunderbird to online or offline status?
- Did you move your (laptop) computer to a different network?
- State your operating system and version. State Thunderbird version from Help > About.
- How often you see the hang (always, rarely, etc)?
- CPU usage - is usage zero, low, high (maxed or pegged), or other?
- ldap address book - do you have an ldap directory address book defined?
- run netstat while Thunderbird is running - any connections to ldap, imap mail server, or other protocols shown for the thunderbird process?
- MS-Windows: open a dos command window (Start, Programs, Accessories, Command Prompt), then type netstat -abo > netstat.log and hit enter. then type more netstat.log to look for lines that show thunderbird.exe.
- linux/Mac: do netstat -tp | grep -i thunderbird
- list the netstat results in your problem report
- If imap connections are seen and if needed by the devoloper, get an imap:5 log in a log file, which can be attached to a bug report
- Steps to reproduce (STR) - Determine a full list of steps which seem to cause the hang. This list is a sequence of actions (1. xxxx, 2. yyyy, 3. zzz, etc) you did just before you shut down. Plus the things you see along the way on the screen. You may need to experiment to find steps that are most reliable, and also eliminate steps which aren't needed to reproduce the problem. If you can't seem to find a reliable set of steps, don't let that stop you from checking the bug list below or filing a bug report with the information you have collected.
- Obtain a hang stacktrace - Please get a stacktrace using Thunderbird symbol server using _hang_ instructions in the references below, then attach text file containing stacktrace to a bug report. Anywhere you see "Firefox" in the instructions, please substitute "Thunderbird".
- Windows: WinDbg instructions, and use "!analyze -v -hang" instead of !analyze -v -f
- Mac: Thunderbird:Testing:Get_A_Debug_Thunderbird_Hang_Stack also Thunderbird:Backtraces_On_OS_X
- Linux: 
- To recap, please concisely report: OS & Thunderbird version, frequency, safe mode results, cpu, netstat results, indexing on or off, pop or imap account types, sleep/hibernate usage, online/offline usage, STR. And, if possible, a hang stack trace.
- All hang bugs: Bugzilla query - open, invalid and fixed bugs from the beginning of time
- Subset: Only open hang bugs: Click the Status column in the query above to order by Status
- Status change: Status of bug has changed recently (4 mo.) (includes unfixed)
- Notable open bugs (from the open bug list:
Caused by other software:
bug 532435Thunderbird 3.0RC 2 does not quit, high cpu, no imap connection and must be killed - with enigmail error [caused by Engimail]
bug 544684Application hang, GUI closed, process not killable from task manager caused by McAfee
- and for more, see INVALID bugs in the "All hang bugs" bugzilla query above
Fixed in development (fixed, but not yet in a released version):
Fixed in version 5
bug 5082633.0b3 hangs on exit/shutdown with high cpu, no imap connections, no ldap connection or stack entry. connection or stack entry after sleep/wake. fixed by closing cached imap connections on sleep, and delay biff restart
bug 524315shutdown hang, high cpu, no open imap connections, no ldap connections but has live, blocked ldap threads
bug 565065- Thunderbird stuck at shutdown, infinite poll gettimeofday read sequence in strace
Fixed bugs in version 3 (most recent at top):
bug 494014shutdown hang, high cpu, no open imap connections
bug 497598hang on shutdown appending msg to imap folder via a filter
bug 487965hang on shutdown with open imap connections and zero cpu
bug 420744Shutdown fails with 100% cpu load when auto-complete over LDAP
bug 495551hang on shutdown, zero cpu, few (1-2) imap connections - from imap url initiated during shutdown (modal alert from imap thread / proxy call to UI thread)
bug 516388Hang when exiting Archives smart folder is used
bug 497059Hang with unreliable wifi connection, either when re-connecting to email server, or on shutdown