With the 38.0.1 update has stopped working IRC accounts
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TB 38.0.1
A fresh install of Thunderbird Portable 38.0.1 and connecting to freenode with a test account works here. Define "stopped working". Any error messages, etc? Did you try creating a new test account on the off chance your old accounts configuration got messed up?
Here a snapshot.
https://www.dropbox.com/s/kz53vdqhtcc6jd8/2015-06-12_171741.jpg?dl=0
I tested with different profiles and all give the same error. The server is fine because with instanbird works well.
I tried also with a clean install to another folder and gives the same error. With TB version 38.0.0 works fine.
With freenode works well
Sounds like a specific issue with TB 38.0.1 then. Note that there was no portable release of TB 38.0. I'd suggest ensuring it fails under a local install (just install temporarily) and then report the issue. It's possible if this IRC uses security, it could be a method that was discontinued in the Gecko engine between 31.x and 38.x of Firefox/Thunderbird.