The Mac App Store has a debug menu just like the most standard Apple applications in OS X. From this menu you can access various of other options such as deleting cookies or the quick search for updates. Close the Mac App Store app and use the following command in Terminal to enable the debug menu.
defaults write com.apple.appstore ShowDebugMenu -bool true
Revert to the default setting with the following command
defaults delete com.apple.appstore ShowDebugMenu