Mozilla Thunderbird, Portable Edition Test is a test version of the popular Thunderbird email client bundled with a PortableApps.com Launcher as a portable app that is being made available for testing purposes only, and is intended for extension developers and our testing community. 

Install Note: This will install alongside a Mozilla Thunderbird, Portable Edition installation by default in a ThunderbirdPortableTest directory. The installer supports upgrading existing installations by manually changing the install location, though this is not recommended.

Download Mozilla Thunderbird, Portable Edition 13.0 Beta 4: http://portableapps.com/apps/internet/thunderbird_portable/test