A quick course in case you didn't know: .mozilla (and any file starting with a dot) are "hidden". There's no actual hidden flag, as there is in Windows, it's just a convention for things like ls so they don't display them. The -h command doesn't mean "show hidden" as it does in Windows either, it means "human readable"; ie, show "1.5M" instead of "1673234".
-a means show all, and is the only way for ls to display "hidden" files like that.
Regarding why the file is on the NAND and the SD card, if I recall correctly, ED made a quick PND of Fenec which just left home where it was, and then at some point updated it with a run script which put the home directory into the appdata folder. Did you perhaps run the first copy ED released and then update a few days later?