I accidentally opened up my main Firefox profile in Firefox Developer Edition and now it won’t let me open it in regular Firefox. It shows a dialog saying “You’ve launched an older version of Firefox” and that things could get corrupted if run on an older version, so the only options it offers are to create a new profile or quit. The new profile was empty, not an import from the existing profile. My solution is to keep using the main profile in Developer Edition for now, disable automatic updates, and then when I get prompted for the next update, decline to run it, open the profile in regular Firefox, and hope that regular Firefox has also been updated and is now above the version that Developer Edition is currently at so that it won’t trigger the version block anymore.