There are two groups of tabs, roughly divided into research tabs and script | mod tabs.
Where an action would open a pak item in the PAK Item tab e.g. double-clicking pak item path text, the item will generally be opened in the PAK Item tab in the 'other' set of tabs. For example, double-clicking a MBIN path in libMBIN API tab (left set of tabs) will open the mbin in the PAK Item tab viewer in the right set of tabs. Likewise, double-clicking a pak item path in a script (right set of tabs) will open the pak item in the PAK Item tab viewer in the left set of tabs.