See if this helps. https://wiki.mozilla.org/Thunderbird:Testing:Memory_Usage_Problems

Thanks, I had worked through this list but to no avail. Anyway, 60.0 breaks too many plug-ins, so I have reverted back to 52.9.1, which was, and is set up exactly as I like it, so no thanks to further upgrades for me.

Something else you can try. Start Windows in 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

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

Does the problem go away?

I didn't try putting Windows in Safe Mode, but with TB60.0 in Safe Mode, the issue went away, so it was obviously one of the add-ons, but I found it impossible to see which one it was by adding them one at a time. Another reason whey I reverted to 52.9.1

Please post your Troubleshooting Information. At the top right of the Thunderbird window, click the menu button , then select Help > Troubleshooting Information. Press the "Copy text to clipboard button" and paste the information into your reply.

Wrt add-on compatibility, it's the responsibility of the add-on authors to keep their add-ons working. So your best bet is to notify the author of a troubled add-on.

Also make sure to read the TB60 release notes. Still functioning add-ons can be restored by changing a pref. https://www.thunderbird.net/en-US/thunderbird/60.0/releasenotes/

Sorry, too late, TB60.0 has been uninstalled.

60.2.1 is out

Thanks for the heads up. I will give 60.2 a go once the other issue is resolved, which is that the 'Manually Sort Folders' add-on, which I find invaluable, does not work under 60. I really don't understand why configuring the UI relies on a third party add on, I would have thought it would have been provided in the native code.

So, tried and trusty 52 is still my way forward for the time being.