Update:
I installed Version: (5.0.0-rc2-dev-720-g9704891c8), release build and now the footprint viewer can be closed.
I have a test project I have been using for learning Kicad. It has two resistors, each shorted out.
Originally both were SMD parts. Today I changed one to a THD. To verify I selected the correct footprint I opened the viewer from Cvpcb. The footprint was displayed but I cannot close the Footprint viewer window.
Windows 10/64
Application: kicad
Version: (5.0.0-rc2-dev-712-g62d6750ce), release build
Libraries:
wxWidgets 3.0.3
libcurl/7.54.1 OpenSSL/1.0.2l zlib/1.2.11 libssh2/1.8.0 nghttp2/1.23.1 librtmp/2.3
Platform: Windows 8 (build 9200), 64-bit edition, 64 bit, Little endian, wxMSW
Build Info:
wxWidgets: 3.0.3 (wchar_t,wx containers,compatible with 2.8)
Boost: 1.60.0
Curl: 7.54.1
Compiler: GCC 7.1.0 with C++ ABI 1011
Build settings:
USE_WX_GRAPHICS_CONTEXT=OFF
USE_WX_OVERLAY=OFF
KICAD_SCRIPTING=ON
KICAD_SCRIPTING_MODULES=ON
KICAD_SCRIPTING_WXPYTHON=ON
KICAD_SCRIPTING_ACTION_MENU=ON
BUILD_GITHUB_PLUGIN=ON
KICAD_USE_OCE=ON
KICAD_SPICE=ON