Im not a mac person. But what you can try at this time is to install a secondary FF but an older one, such as version 78. Then with the current FF closed down (or simply uninstalled), launch the older version of FF and try logging into your sync account. With any luck, it will get updated with your user data. There is also something to keep in mind. Just because you are no longer using your old laptop, its hard drive can become an external hard drive for your new laptop whereas you can store files and back ups on it. But most importantly, you may be able to copy your old FF profile over to the new computer.