when I preview an email that has inline base64 elements, or open an attachment, it takes several minutes. As long as I open mails in the same folder, no more delays opening emails containing base64 content or opening attachments. Moving to another folder, same delay on first encounter of base64 decoding. If I move to another folder, opening an email without base64 content (no delay) and then move back to the previous folder, no delay. It seems that thunderbird, on first encounter of base64 content, decodes all base64 content in the folder and caches it. Moving to another folder and encountering base64 content clears the cache, decodes all base64 content in that folder and caches it? This problem seems to have appeared since version 60.4. No add-ins envolved, tried safe mode.