Whenever I start Firefox, it opens a window with tabs I used from a previous session, which is what I want since I set it on Tools > Options > When Firefox starts. However, whenever I open new windows after I have opened Firefox, it always opens four tabs along with my homepage. I tried deleting the four tabs from history then opening a new window again, but it still opens five tabs in the new window. This started around last week. And I don't think I did anything different. I was just surfing the net as usual.