Hi Saad, Firefox [https://www.mozilla.org/en-US/firefox/72.0/releasenotes/ version 72] replaced the notification pop-up with a speech bubble on the address bar. More about that and your notifications settings [https://blog.mozilla.org/firefox/block-notification-requests/ here]. Desktop notifications in Windows 10 are discussed here: Change notification settings in Windows 10 https://support.microsoft.com/en-us/help/4028678/windows-10-change-notification-settings

Also, take a look at this: Enable/Disable Mozilla Firefox Notifications to Show in Windows 10 Action Center https://www.askvg.com/tip-enable-disable-mozilla-firefox-notifications-to-show-in-windows-10-action-center/