How to remove new profile created by Firefox during an update?

Firefox created a new Profile for me during a recent update and ignored the Profile I had been using for many years. That probably occurred because Firefox couldn't find the original Profile. I had moved it to C:\0-FFox\ to shorten the length of file names. I had been getting File-Name-Length errors, which ended after moving the Profile closer to C:\. Now I can't access or use the original Profile. I've researched the ins and outs of Profiles but can't find a solution to this problem. I want to add my old Profile to the new Profile created by Firefox and maybe switch between the two, or maybe revert to using only the old Profile. But I can't figure out how to do that. Adding a Profile seems to imply adding a '''new''' Profile and not an old one. I sincerely hope you can help me solve this problem! Many thanks! Wayne