How to download older version of Thunderbird?

Thanks. Is there a procedure for transferring all the settings from one Thunderbird installation to another, especially the account data?

Try this to revert to the prior release:

   Exit Thunderbird if running.
   click windows key and 'r' key
   Enter: thunderbird.exe -P --allow-downgrade
   click on 'OK

Unfortunately I thought I would install a parallel installation using the older version but I screwed up and clicked the update button which appears to have installed the old version over the existing version. I am now involved in recovering a complex setup that evolved over three or four years. I suppose there is a silver lining but it is hard to see it. Thanks for the response.

Give details on what is happening, such as error messages. You've lost nothing, so far. does thunderbird start? tell details

It is requesting account setup information. But your followup did inspire me to calm down and 'think'! I have a Thunderbird backup folder. However, I have never tested it but I gave it a shot today and Thunderbird doesn't like the zips in it. Somehow that doesn't surprise me. However, I also have backups of the program folder and Thunderbird's appdata folders that were current a couple of days ago. I should be able to recover the installation from there.... except that there is likely to be some issues related to differences between the 154.0 and the 149 profiles that will mess up that plan?

Uhhh... while I was messing about with this issue Thunderbird updated itself back to 155!!! Grrrr...

click to settings>general and reset to NOT UPDATE AUTOMATICALLY and then follow my prior post

Thanks. Disabled auto update earlier. I will do your steps. Appreciate your patience.

I have the basics back and, assuming I can remember where I put everything, I should be able to recover my data. The "Create a new profile" requirement is a bit of a wrench in the works. I will avoid auto-update in the future and maybe my configuration will survive more than 4 or 5 years. Thanks for the help. evan