How do I get my window back?

A few days ago, I left the computer alone for a few hours and, when I came back, the window that has all my online tabs open was gone! I tried to open a new one so I could tell it to re-open all the tabs I had open when I was last here but, I couldn't find that command anywhere! So, I tried open the tabs manually. Apparently, the old one is still open SOMEWHERE because, every time I get a new e-mail, I hear the bell ring twice! How do I get the older one to come to the surface again?

How do I get my window back?
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