The format of the profile files in the various versions of Windows is identical. For details of the files that you can copy between profiles see https://support.mozilla.com/kb/Recovering+important+data+from+an+old+profile There is one profile file listed in that article that I would not copy, mimeTypes.rdf, as that one will store details specific to the operating system. Future versions of Firefox may change the format of the files used, this has happened occasionally in Firefox development and meand that the files are not backward compatible, so you can not always use them with an earlier version of Firefox.