joomlaXplorer is an extremely handy tool if you don't have access to ftp or a file manager like cpanel. Once I accidentally deleted a template file but couldn't remove the directory because it was assigned to "nobody".
I couldn't remove the folder via ftp or cpanel file manager, but joomlaxplorer came to the rescue and was able to delete it anyways.
My only criticism is regarding the interface. The icons for managing files and directories are without any text unless you roll your mouse over the actual link. You have to guess a bit until you learn which icons do what.
An option to show or hide text/icons would be very handy. None the less, this small complaint does not outweigh the handiness of this extension's great built-in browser. 4 out of 5 stars.