I had ESR and regular Firefox installed so that I could use Google Hangouts last year after they dropped plugin support. After a particular upgrade (don't remember which), all of my data just disappeared because the profile formats were different and Firefox decided that the file was corrupted.

Thankfully I figured out what was going on, and they saved a backup of the "corrupted" file that I could just put back into place.

It seems like absolutely the correct solution to have each release to have its own profile.