In earlier versions of Lightning there were Javascript files (amongst others) in a subfolder called "chrome" which allowed for tweaking. Under Linux, the item window was minimizable by default, not under Windows. THis could be changed by modifying the appropriate Javascript file: C:\Users\<account_name>\AppData\Roaming\Thunderbird\Profiles\jzmyuqgz.default\extensions\<Lightning folder>\chrome\calendar\content\calendar\calendar-item-editing.js Version 4.0.1 of Lightning does not have a "chrome" subfolder, but a file chrome.jar. It seems, the resources have been compiled into the JAR file, which makes it pretty impossible to make changes. Currently I can't even view the contents of that file with "jar tf chrome.jar" Does anybody know about another way to get the item windows minimizable?