Where do I download v31 of Thunderbird?

I have used Thunderbird for some years. I recently installed the add-on Lightning. In order to do that I had to update my version of Thunderbird to the newest, which I think is v34. I have had nothing but trouble .. some emails coming in, others not. My printer won't respond, etc. etc. Finally got fed up and uninstalled Thunderbird completely. Now I want to install a previous version which seemed to work ok and I will not install Lightning. But I cannot find where I can download a previous version. So my questions are, where do I find a download for a previous version and if I do, will this solve the problem?