At the start-page (file:///usr/share/doc/python-docs-2.7.1/html/index.html) there is a link 'Global Module Index' (left column, first entry in 'Indices and tables'). It points to non-existent page 'file:///usr/share/doc/python-docs-2.7.1/html/modindex.html' The 'modules' shortcut at the top-right, which should point to the same page points to a working page 'file:///usr/share/doc/python-docs-2.7.1/html/py-modindex.html' (note the additional "py-" prefix in the filename).
*** This bug has been marked as a duplicate of bug 670493 ***