Edit:
Never mind - finally found it in File Manager > Edit > Preferences.
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Somehow I screwed up my mouse settings in the Raspbian GUI. Back when I first installed Raspbian I found a way to single click on an icon to open the associated file. Now something has gone wrong and I can't open anything on the GUI with a single OR a double click. I have to right click and click open to open a file etc. I have tried for hours to remember where I originally found the setting to change the default double click to a single click. I could have sworn the settings for the mouse clicks were in Openbox configuration. Help is appreciated.