The main focus of my issue is that Firefox's sudden new behaviour of it opening normally when it launches, with my previous tabs remembered as I set is immediately followed by the browser quickly re-launching within seconds. While this isn't a big concern when I open Firefox from its shortcut, it's become a serious issue when I launch Firefox from an external URL, like from an email, or when viewing an original picture posted in a Discord chat channel.

When the relaunch happens, it's always without the tab that caused Firefox to launch automatically on clicking said external URL. I realize that I need to do an addon check, but that's a long process, so I was rather hoping this was a known issue that someone knows the solution to, or what addon is involved and how.