Hello there Yes, it is possible that older versions are slower than newer versions and can also be slower with the newer versions, even if it is not a myth, even when used with very fast new hardware like SSDs. The old-fashioned answers are a large number of files in the inbox. Corrupted files can create that situation as if there is a corrupted msf.file that can bring slowness there and it can suddenly appear. About Thunderbird's parameters, there are no new parameters or different sets, bug fixes and platform updates that determine the difference between versions. If you were to ask us what parameters there have been for different Thunderbird versions lately? The latest information on both versions can be seen on the Thunderbirds page on the internet. When I read these pages there, it sounded good to me when I read them. https://support.mozilla.org/en-US/kb/thunderbird-release-notes-whats-new-and-known-issu Greetings googlethunderbird.