As far as I know, “import” is only for pulling data from other browsers, not from other instances of Firefox. I skipped that step, and it created a new default profile.
If you go to about:profiles, you should see all the Firefox profiles on your system. It will indicate which you are using. On my installation, Firefox Destiny created a new profile.
I think, however, that the profile-creation may be related to the filename and location. For myself, I renamed the app from “Firefox” to “Firefox Dynasty”. If you left it as the default “Firefox” name and/or moved it to Applications (overwriting your ESR installation), then it might be trying to use the same profile as before. That much should be obvious.
In my case, after noting the locations of the two profiles, I quit Firefox and replaced the contents of the new profile folder (used by Dynasty) with a copy of everything in my old profile folder (used by ESR). That worked for me - Dynasty probably upgraded the profile, as new Firefox releases always do, but it worked, including my various add-ons (which I think are installed to the profile directory).
Be sure you do not do this while any installations of Firefox are running or you may corrupt the profile!
If you want to experiment with profiles, you can manually launch Firefox with the -P option to view its profile manager. You can interactively create, destroy and switch profiles this way. Do it from a terminal window:
$ /Applications/Firefox.app/Contents/MacOS/firefox -P