In VS2012 when you select a file in solution explorer it automatically opens file in a special \"preview\" tab.
Maybe my computer is not fast enough, but this previe
In Tools > Options > Environment > Tabs and Windows, you can disable it by unckecking "Solution explorer" under Preview tab.
I find it using the "Quick launch" new feature. Simply type "preview", and a link to the setting will be suggested. Great new feature of VS