I have 3 monitors, with Thunderbird on my center monitor, which is the primary display on a Windows 10 box. I have two calendars (Gmail and work) that are managed by the Lightning calendar extension for Thunderbird. When I receive a meeting invitation and I click on the Accept button, I am prompted with a "Select Calendar" popup to select which calendar I want to add the meeting to. Unfortunately, the popup is small (under 300x300) on a very busy screen and always shows up in the very top-left corner of my left monitor, which is usually -just- out of my peripheral vision, so it can feel like Thunderbird simply didn't register my click of the Accept button. Usually after about 5-10 seconds and a second click, my memory kicks in and I check for the accept pop-up and so I'll turn my head and see that tiny popup showing in the top-left corner, and then I can click on the correct button in the popup. It would be very helpful if this Select Calendar popup would simply show up next to the Accept button or (worst case) wherever the mouse cursor happens to be.