Forum der Gemeinschaft Thunderbird

I'm trying to get the calendar app working in a new Thunderbird installation. Here are my notes on what I tried: https://addons.thunderbird.net/en-us/thunderbird/addon/lightning-calendar-tabs/versions/ Download lightning_calendar_tabs-3.8-tb.xpi (latest version) to C:\Users\ken\Downloads In Thunderbird: Tools --> Add-ons --> Gear icon --> Install add-on from file --> C:\Users\ken\Downloads --> lightning_calendar_tabs-3.8-tb.xpi "about:addons Lightning Calendar Tabs could not be installed because it is not compatible with Thunderbird 144.0.1." Any suggestions?

Can someone explain why the emails I write are still spell-checked, even though I have unchecked "Check spelling before sending message" and "Check spelling continuously" in "Settings" countless times? Even the Thunderbird add-on "Replywithheader" still checks spelling, even though I have unchecked "spell-check" there too. I don't want spell-checking, but I can't get away from it! It really bothers me.