I am running Thunderbird version 128.11.0esr (64 bits) on Windows 10 Pro. I have defined, in Windows, the default program for .doc and .docx files to be LibreOffice Writer and this works fine when I click on such a file in Windows. But when I got a docx attachment in a Thunderbird email, and clicked on it, nothing happened. When I right-click on it, it just offers to open (not to select which program to open it with). I have to save the file locally, and click on it in Windows in order to open it. This is very frustrating, all the more so that it used to work. I tried adding the two following lines to the prefs.js file, to no avail - no change: user_pref("network.mime-handler.external.application/vnd.openxmlformats-officedocument.wordprocessingml.document", "D:\\Program Files\\LibreOffice\\program\\swriter.exe"); user_pref("network.mime-handler.external.application/vnd.openxmlformats-officedocument.wordprocessingml.document.useSystemDefault", false); Any suggestions? Thanks!