You can download the previous version from ftp.mozilla.org and install it. After reverting to your previous version you can check your crash reports to see what was causing the problem via Help -> Troubleshooting Information...

Brucee said

I just upgraded to Thunderbird 31.3.0 (on Windows 7). Now I can no longer launch Thunderbird. It just shows the Mozilla crash reporter every time. How do I recover from this? Is there a way to revert to an earlier release?

Thanks. I believe I traced the problem to one of the addons. They all worked with the previous release, but one of them is preventing 31.3 from starting.