https://forums.opera.com/topic/28783/open-popup-screen-center/1?lang=en-US
open popup screen center | Opera forums
Sep 22, 2018 - Hello, I need to open the popup windows of a website in the middle of the screen. They open up to the left. How can I do? Thank you.
open popupscreencenteroperaforums
https://www.dktpakistan.org/
Auto Open Popup Example
auto openpopupexample
https://bugzilla.mozilla.org/show_bug.cgi?id=1206885
1206885 - [e10s] Firefox x64 doesn't open some Popup-Windows
RESOLVED (mconley) in Core - Widget: Win32. Last updated 2016-06-13.
firefoxopenpopupwindows