Please start *Windows'* safe mode with networking enabled - win10 https://support.microsoft.com/en-us/help/12376/windows-10-start-your-pc-in-safe-mode - win8 https://support.microsoft.com/en-us/help/17076/windows-8-startup-settings-safe-mode - win7 https://support.microsoft.com/en-us/help/17419/windows-7-advanced-startup-options-safe-mode#start-computer-safe-mode=windows-7 - XP https://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/boot_failsafe.mspx

Still In Windows safe mode, start thunderbird in safe mode - https://support.mozilla.org/kb/safe-mode-thunderbird

Does problem go away? Please reply to let us know results.

Thank you Wayne.

I did what you said: - Started Windows 8.1 in safe mode with networking enabled - Opened Thunderbird in safe mode

The problem went away. All draft saving was very quick (a fraction of a second, after the first save which took about a second), even when I'd typed a longer message.

Please can you help me to make it speed up in normal mode?

> Please can you help me to make it speed up in normal mode?

The typical cause is antivirus software. If you start Windows in safe mode and Thunderbird in normal mode, and see the problem, then the cause is something loaded when Windows starts.

OTOH, if you start windows normal and Thunderbird in safe mode and the problem is seen, then cause is something loaded when Thunderbird starts - typically an addon.

Let us know what you find.

> Let us know what you find.