In my experience, just copying an existing profile to a new folder doesn't work -- you're backing up your data, but you're not creating a new profile. So what

In my experience, just copying an existing profile to a new folder doesn't work -- you're backing up your data, but you're not creating a new profile. So what I typically do is first create a new profile via Firefox' UI, then I just copy the data of the profile I want to clone into the corresponding data folder of the profile I just created.