Download and install the current release from https://www.mozilla.org/en-US/thunderbird/all/ There is no Thunderbird 64 bit build for Windows, and you actually don't need one.

Where in the world did you get thunderbird-31.3.0.en-US.win64-x86_64 ?

Wayne Mery said

Where in the world did you get thunderbird-31.3.0.en-US.win64-x86_64 ?

Hey Wayne, Did a Google search and found it. Did not know there were no 64bit versions for Firefox or Thunderbird. Been using Linux Mint for a long time and just recently started using Windows on a new laptop. Now using to current 32bit Thunderbird, but have installed the 64bit Developers Edition of Firefox. Guess I miss using the 64bit versions in Windows 64, a little anxious I am.

Perhaps in version 45. But for now, no supported 64 bit Thunderbird is available.

dwflo said

Did a Google search and found it. Did not know there were no 64bit versions for Firefox or Thunderbird. Now using to current 32bit Thunderbird, but have installed the 64bit Developers Edition of Firefox. Guess I miss using the 64bit versions in Windows 64, a little anxious I am.

There are 64-bit Firefox for Mac OSX and Linux since Firefox 4.0 because it was much easier and also needed to run.

The earliest for Win64 Release for Firefox may be 42.0 unless it changes again as 41.0 was the last target until some sandbox issues.

There are four main development channels for Firefox. A new version is started in development on Nightly and move/merges to next channel when a version is Released. The Beta, Aurora (aka Developers Edition) and Nightly channels for Firefox have Win64 builds but not Release yet.

Release < Beta < Aurora (aka Developers Edition) < Nightly

Beta channel can get six to twelve builds for a version. While the Aurora and Nightly channel get checkins almost everyday so those channels gets updates each of those days.

Beta channel currently has 42.0b9 (beta nine build), Aurora has 43.0a2, Nightly has 44.0a1. When Firefox 42.0 is Released the versions will move/merge to next channel.

The Aurora (Developers Edition) build you have was likely a random build of 41.0a2 when 41.0 was being worked on on that channel. It is not close to being same as the 41.0 Release.

I think I know the third-party site you grabbed these builds from as they just post a random WIn64 build when the version changes on a channel.

As you can see, random builds. http://www.m64.info/