When did you first install Lightning or have it installed? I am running Windows 8.1 64-bit; history and details are as follows: 1.) Yes, I have been using TB 31.x (and also earlier versions) before.
The admin account (from which TB was installed) never had the Lightning extension installed, while the (non-admin) user account had several versions of Lightning installed and enabled.
Example: launch/exit crashes, features missing, etc. User Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:39.0) Gecko/20100101 Firefox/39.0 Build ID: 20150630154324 Steps to reproduce: 1.
Sharing the same Thunderbird profile between different versions of Thunderbird (e.g., 2.0 and 3.0) may cause problems.
As long as you avoid sharing a profile between versions (something which applies to the above method, as well), Mozilla builds are safe to use, since they have undergone extensive QA prior to release.
https://support.mozilla.org/en-US/questions/1073862 Removed after 38.1 back after 38.2 I am sure there are more as this was not the one I went looking for.
1.) Not at the moment, as all production machines have already been updated and the testing machines have no internet connection, so over-installing is the only option. Maybe someone else could step in and test it with automatic updating in the meantime.