The standard way to search for problems is to click Open Problem Library (actually it should already be selected so it will greyed out when you open the Library Browser) and select a Subject, Chapter and Section and then hit View Problems. You can also click on Advanced Search which gives you more options. Older versions of WeBWorK use the terminology National Problem Library (NPL) instead of Open Problem Library (OPL).
You are certainly correct that using the method that accesses the directory structure of the libraries (OPL Directory and, if they are set up, Contrib, CAPA, etc) produces a long list of directories. It is designed for people who know exactly what they are looking for (and where to look). It is also useful for people who want to find problems written at a certain institution (Union, Michigan, Rochester, etc). Finally it is the only way to access problems that are not in the OPL (e.g. because, in the case of CAPA, they are not tagged or, in the case of Contrib, they have been recently submitted and have not yet been accepted by an editor for inclusion in the OPL).
Arnie