In blend 4 i often open a resource dictionary (i.e. "Generic.xaml") by clicking the "resources" tab (next to the property tab on the right pane), navigate to a resource and click on its icon to edit it in the designer.
In blend for visual studio 2012 i can't seem to find the resources tab? How am i then able to edit resources in resource dictionaries?
I'm assuming this is a XAML project. Is the Window open? Main toolbar -> Window -> Resources... is that checked? If not, check that.
As of VS2012 Update 2+ we can once again create desktop WPF apps so the Resource tab returns.
"In addition, Visual Studio 2012 Update 2 and later adds support for Silverlight and WPF editing, as well as SketchFlow. Developers can now leverage a consolidated tool for all the platforms as part of a fully integrated solution with Visual Studio." (1)
(1) "Microsoft Expression Changes", http://www.microsoft.com/expression/eng/, retrieved 2013-9-20