1) If your mouse has a back button, you can use it to move back. Otherwise, bind the keyboard shortcut to "View.NavigateBackward" (Edit: default binding is Ctrl + - ). Or click this button:
2) This is not possible without any kind of extension; Visual Studio does not support this out of the box. The best you can do is find all links on an interface, and the results of this should include every class that implements this interface.
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