That's very strange. The app.update.channel pref should control the
channel, so I think you're really still on the release channel, but I
can't explain why your about:firefox says you're on the esr channel.
Do you have app.update.desiredChannel set? It shouldn't be used any
more, but I guess there's a chance it's hanging around.
Also, in your Fx program directory (not the profile directory), do you
have any .js files with app.update.channel in them? I think they'd
live in a subdirectory called defaults, but I'm not sure for Windows. I
wouldn't monkey with those files, I'm just curious about what they say.
Firefox no longer supports channel switching; the recommended way to
get in the channel you want is to download and run the full installer.
That would probably fix this weirdness for you.