Firefox profiles no longer work in Tor Browser 15.0

They used to work in Tor Browser 14.5

Now Tor Browser crashes if creating a new profile, either in about:profiles or using the standalone profile manager by launching /Applications/Tor Browser.app/Contents/MacOS/firefox -P on macOS.

When trying to create a new profile, the new profile folder is actually created in the profiles directory (TorBrowser-Data/Browser/), but the profile won't show up in the profiles list when re-launching Tor Browser. It also is not added to TorBrowser-Data/Browser/profiles.ini.

Disabling the setting "Use the selected profile without asking at startup" in the standalone profile manager also causes Tor Browser to crash and the setting is not disabled when Tor Browser is re-launched

If Tor Browser is already running, then launching a second instance using the Terminal command /Applications/Tor Browser.app/Contents/MacOS/firefox causes it to briefly open with the following error:

Close Tor Browser A copy of Tor Browser is already open. Only one copy of Tor Browser can be open at a time.

I'm on macOS 11 Firefox profiles support page: https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles