Hi, I´ve installed Thunderbird today, clean installation (no prior installation). So it´s 128.7.1esr (64-bit) version on top of my Windows10 Pro fully updated. I´ll use Thunderbird just to manage my personal agenda in Calendar, I won´t be using the email part so I didn´t configure the email client. When I create a recurring event with due date "forever" the app starts lagging so badly, and when ir finally creates the events, if I change any of them (for example I drag it to another hour) the whole app freezes and I need to close it from Task Manager. I´ve tried to let it working for a while, and when I´m back it eventually completed the change, but I don´t know how long it takes. After closing with TaskManager, I see the change has been applied. I´ve followed this instructions to run in Troubleshoot Mode https://support.mozilla.org/en-US/kb/troubleshoot-mode-thunderbird#w_start-thunderbird-in-troubleshoot-mode And it works!! in Troubleshoot Mode, and more specifically disabling add-ons the Calendar works just fine. BUT, the problem is, I´m using a clean installation: I haven no add-ons at all, and only the 3 default themes that can not be deleted/disabled. How can I fix this? or I´m forced to enter in Troubleshoot Mode every time? Maybe a previous version is better for using the Calendar alone, without an email account? BTW I´ve dissabled the hardware acceleration, just in case, but it didn´t help. Thanks for your help!!!